A noun is a person, place, thing, or idea. My own German teacher used to say that a noun is something you can theoretically touch. In German, all nouns are capitalised. So if something is capitalised in the middle of a sentence, it is a noun or a word that functions as a noun.
A pronoun replaces a noun in a sentence and refers to a previously mentioned noun (for example, when talking about John, we can say "er/he" instead of using his name again). It has the same function in a sentence as a noun and can be the subject, direct object, indirect object, or the object of a prepositional phrase.
The subject of a sentence is almost always a noun or pronoun. It is the person or thing that performs the action of the verb in the sentence. A subject is always in the Nominative case.
The direct object is the "do-ee" of the sentence, that is, the object with which something is done. Again, it is almost always a noun or pronoun. A direct object is always in the Accusative case.
The indirect object is a noun or pronoun that answers the question "to whom" or "for whom" the action is performed - the recipient of the direct object. A indirect object is always in the Dative case.
The verb is the action of the sentence and describes what is being done. IN GERMAN, THE CONJUGATED VERB IS ALWAYS IN THE SECOND POSITION IN A MAIN CLAUSE! In other sentences (with conjunctions like dass or weil), the verb is at the end of the sentences. In general, we expect verbs to be accusative verbs if not clearly stated as Nominative verbs (sein, werden, bleiben) or Dative verbs (geben, schenken, danken...)
An article is used to indicate whether the noun refers to something or someone specific or to a general group. A definite article ("the" in English) refers to a certain, specific noun. In German, these are "die," "der," and "das" as well as all their various case and gender forms (dem, denen, etc.). An indefinite article ("a" or "an" in English) refers to a noun whose exact identity is unspecified; not the bird (that bird there specifically), but a(ny) bird. Other types of articles, e.g., demonstrative articles such as "dieser" and "jener," have a similar specifying function. Dieser, mancher, jeder, etc. are demonstrative articles in German and follow the same rules as definite articles (der).
An adjective describes a noun or pronoun by answering the question "how?". For example, der "gute" Wein, the good wine.
A preposition indicates the relationship of a noun or pronoun to another word in a sentence.
Example: Der Hund sitzt auf der Mauer. The dog sits on the wall.
Prepositions answer the same kinds of questions as adverbs. A preposition is used with a noun to form a prepositional phrase:
Der Hund sitzt auf der Mauer. Wo sitzt der Hund? Auf der Mauer.
In German, prepositions can place their objects in the accusative, dative, or genitive case.
A conjunction connects words or groups of words. Some conjunctions in German are aber, oder, und, weil, and dass.
An infinitive is the base form of the verb that has not been changed to indicate tense or to have endings. In German, an infinitive almost always ends in -en or -n and is the form of the verb that is in the dictionary (e.g., machen, gehen).
Conjugation simply refers to a set of endings (and sometimes vowel changes) for verbs that are used to indicate person and tense. For example, sein: ich bin, du bist, er sie es ist...
Person is a term that describes the "point of view" of a sentence. There are three "persons" referred to as 1st, 2nd, and 3rd. The 1st person is used when the speaker of the sentence is the same as the subject of the sentence. In this case, the subject is either the singular form I (I) or the plural form we (we). The 2nd person is used when the speaker of the sentence is directly addressing another person. The subject is then the singular you (you) or the plural you (all of you). The 3rd person is used when the speaker of a sentence is talking about the activities of someone else who is not being addressed directly. It is the most common person and is used for ALL NAMES. The 3rd person pronouns are er (he), sie (she), es(it), and sie(they).
Gender: In German, nouns are distinguished by their gender. There are three genders: masculine, feminine, and neuter. The gender (and number) of a noun determines the endings for indefinite articles and adjectives, and also the form of the definite article.
There are a few generalizations that can be made, but most have exceptions. There are very few rules that don't vary: Any noun ending in -lein or -chen is a neuter, any noun ending in -in, -ung, -keit, -heit, -tät, -ie, -tion is a feminine, and any noun ending in -mus or -ig is a masculine. For compound nouns, the last word in the compound determines the gender of the entire word.
das Bier + der Garten = der Biergarten