The verb is a word that is used in the main speech to express an opinion or action. The verb can be in the infinitive. When it is conjugated, most often an ending is attached to the verb stem. The verb stem is the root of the verb, a part that does not change.
In German, verbs can be transitive or intransitive. It is important to know the difference between the two: transitive verbs can be followed by a direct object complement whereas intransitive verbs cannot.
Some verbs are reflexive. They are accompanied by a reflexive pronoun that represents the same person as the subject, for example:
setzen: Ich setze mich (I sit down)
Finally, some verbs are impersonal. They are only conjugated in the third person of singular. The best example is, as in English, the verb regnen (to rain) which gives in the present tense:
regnen: Es regnet (it rains)
Weak verbs are not a problem once the endings are known. Strong verbs need to be memorised in order to know the irregularities.