There are seven modal verbs. These are verbs that are common when speaking or writing and do not express an action by themselves, instead they support another verb. The modal verb always takes the place of the main verb placement in the sentence, while the main verb gets relocated at the end of the sentence.
Ex: I have to go to the city.
Ich muss (I have to) in die Stadt (to the city) gehen. (go)
Ich muss in die Stadt gehen.