GERMAN AUXILIARY VERBS

Definition: Auxiliary Verbs are literally helping verbs such as modals, sein(to be) and haben(to have), and werden(to become) are used as auxiliary verb:

SEIN:
sein, bin, bist, ist, sind, seid, war, warst, waren, wart, wäre, wärest, wären, wäret, sei, seist, seien, seiet.

HABEN:
haben, habe, hast, hat, habt, hatte, hattest, hatten, hattet, hätte, hättest, hätten, hättet.

WERDEN:
werden, werde, wirst, wird, werdet, wurde, wurdest, wurden, wurdet, würde, würdest, würden, würdet.

German never uses a form of do as an auxiliary. Forms of do are used only for the main verb.

Examples in German:

I never do that.
Ich tue das nie.

I do [am doing] my homework.
Ich mache meine Hausaufgaben.

German never uses a form of sein to express a progressive tense:

Examples in German:

was singing = sang

habe gesungen

German uses werden instead of sein to form the passive voice.

Modal auxiliary verb.
In German there are six modal verbs (Modalverben), which are very commonly used and are the equivalent of English modal auxiliary verbs can be conjugated in relation to the present, the past and the future and they share a common pattern of conjugation. These verbs modify the meaning of a main verb by introducing notions of obligation/probability, possibility, and permission. The modal verbs in German are:

can, to be able to	können
must, to have to, be required to	müssen
will, to want to, plan to	wollen
should, am to, ought to, to be supposed to	sollen
may, to be allowed to, be permitted to	dürfen
to like, to like to, care for	mögen

The modal verbs are almost always used with another verb, which is required to complete the meaning.

Examples in German:

I am not allowed to go to the disco.
Ich darf nicht in die Disko gehen.

Can you help me?
Kannst du mir helfen?

When is he supposed to arrive?
Wann soll er ankommen?

More:
Reflexive Verbs