This short article provides a brief overview of the parts of speech in German. It is meant as a review.
Nouns: nouns are people, places and things. They can be abstract or concrete, singular or plural, or even collective (singular in form, plural in meaning). In German every noun has a gender (masculine, feminine, neuter), which may or may not correspond to its "natural" gender (boys are masculine, but girls are "neuter" because the word for girl is the diminutive of "maid", and all diminutives are neuter)—after all, what gender should a rock, a star, or freedom have? Nouns can be the subjects and objects of verbs, as well as the objects of prepositions.
Verbs: verbs are words of action or state: "to be", "to have", "to eat", "to live", "to die". In German verbs can be either transitive (they can take a direct object) or intransitive (they don't take a direct object). Examples of the latter include verbs of motion and of state (to go, to be). In German verbs have two simple tenses: past and present. All other tenses are "compound"—made up of a "helping verb" (werden, sein, haben) and either a past participle or an infinitive.
Infinitives: in German the infinitive is a "base" form of the verb that ends in "en". If the verb is "go", the infinitive is "to go"—gehen, for example. If the verb is "have", the infinitive is "to have"—haben. Infinitives are used in some compound tenses, such as the future, with a helping verb. Infinitives are "infinite" in the sense that they don't have a "tense" (fixed time) or "person" (a subject performing the verb), so they are not "bound", "limited", or "finite"—hence, "in-finite". Conjugated verbs are called "finite verbs".
Participles: participles are "part" of the verb, and they are a different part of speech. That is, they come from the verb, but they cannot be used as verbs (they don't have "subjects", for example). They are often used as adjectives in German. German has two types of participles: present and past. The present participle corresponds to "ing" words in English (flying, eating, dying), whereas past participles correspond, usually, to "ed" words in English (flew, ate, died). Past participles in German are used in compound past tenses with a helping verb.
Articles: nouns can have articles in front of them, either definite, or indefinite. Definite articles (e.g. der, die, das) mean "the"; indefinite articles (e.g. ein, eine) mean "a" or "an". The article matches the gender of the noun, and so it is best to learn the definite article when learning the noun so as to remember the gender. There is a plural definite article (e.g. die), but no plural indefinite article.
Pronouns: pronouns stand in for nouns. They have person (1st, 2nd, 3rd) and number (singular, plural). In the nominative, the personal pronouns are ich, du, er/sie/es, wir, ihr, sie, and Sie. There are also reflexive pronouns (mich/mir, dich/dir, sich, uns, euch) that basically mean "yourself", "himself", "herself", etc. We often speak of the "possessive pronouns", which are actually "possessive adjectives"—we say 'pronoun' because like real pronouns they have person and number and stand in for the person who owns/possesses something (my, your, his, her, our, their)—mein, dein, sein, ihr, unser, euer. They are, however, adjectives (they modify nouns), and take adjective endings.
Adjectives: adjectives are words that modify nouns. They answer the question "what kind?" For example, if you have a house (noun), what kind of house is it? Is it red, big, old? The possessive pronouns/adjectives (see above) answer the question "whose?" Adjectives can be either attributive or predicative. You use predicate adjectives when you say "the house is red" (das Haus ist rot)—it equates one thing (a noun) with another (a quality, an adjective). If you say "the red house" (das rote Haus) you are attributing the quality red to the house—that is, attributing a quality to a thing. Attributive adjectives take endings in German, and these are determined by the gender, number, and case of the noun being modified.
Adverbs: adverbs most often modify verbs and adjectives, but can modify prepositional phrases, other adverbs, and whole clauses. One can run (run is the verb), or one can run quickly (run is the verb, quickly the adverb). You can have an egg (noun), a cooked egg (egg is the noun, cooked the adjective), or a well cooked egg (egg is the noun, cooked is the adjective describing what type of egg, and well is an adverb describing how it is cooked). Adverbs often answer the questions "how?" "when?" or "where?" Three main categories of adverbs, or adverbial phrases (a collection of words that acts as an adverb) are those of time, manner, and place (when, how, where—see above), and in German they occur in a sentence in the order time, manner, and then place ("Jeden Tag lese ich langsam die Zeitung zu Hause.").
Conjunctions: conjunctions serve to bind phrases and clauses together and describe the relationship(s) between them. In German there are two types of conjunctions: coordinating and subordinating. A coordinating conjunction "coordinates" two equal phrases: bread and butter, white wine or red. Examples include und, oder, aber, and denn. Subordinating conjunctions subordinate one phrase or clause to another. This often indicates a logical or causal relationship, as in "I stayed home because I was sick."—the two are not equal: I didn't just stay home, and I wasn't just sick, but the reason that I stayed home was because I was sick. Examples in German include weil, als, wenn, wann, ob, and nachdem. Most of the interesting conjunctions in German are subordinating. Subordinating conjunctions induce "verb at the end" behavior; with coordinating conjunctions the verb in each clause is in the 2nd position.
Prepositions: a preposition comes before a noun or noun phrase and indicates a relationship between that noun phrase and the rest of the sentence. The combination of preposition and noun phrase is called a prepositional phrase. German has 5 prepositions that cause the following noun to be in the accusative case: durch, ohne, gegen, für, and um (DOGFU), and 8 that cause the following noun to be in the dative (aus, ausser, bei, mit, nach, seit, von and zu—they can be sung to the tune of J. Strauss's "Blue Danube Waltz"). In addition there are a number of "two-way" prepositions that sometimes take the accusative and sometimes take the dative (in, auf, an, über, vor, neben, zwischen, unter, hinter) depending on how they are used. Not to to be forgotten are a number of prepositions that require the genitive; the most common are trotz, während, statt, and wegen (note: in reality, the vast majority of German prepositions take the genitive, but they are rarely encountered, and furthermore, the genitive is dying out—most people use the dative with "genitive" prepositions in normal speech).
Postpositions: a preposition is called such because it is positioned before the noun it governs (hence, pre-position); German also has a few postpositions—that is, words that come after the noun they govern. The two most common are also prepositions: entlang and gegenüber. When entlang is used as a preposition, it takes the dative ("entlang der Straße"); when it follows a noun, it takes the accusative ("die Straße entlang). Gegenüber always takes the dative, but can come before or after the noun it governs (but always after a pronoun)—"ich saß dem Mann gegenüber", "ich saß ihm gegenüber", "die Post ist gegenüber dem Bahnhof", die Post ist dem Bahnhof gegenüber".