Let‘s build some basics – let’s get to know the three most important German verbs:

sein (to be), haben (to have) and werden (to become, to get).
 
All three are irregular verbs.
 
And the reason why you want to know them by heart is: they are used to build most of the tenses in German.
So if you want to talk about the past or the future, you’ll have to use them.