Verbs like to want to, must, can are important verbs, but they are different in a way that the following examples show best.
I must swim.
I can swim.
I want to swim.
The verbs to want to, must, can somehow changed the tone of the activity. This is what modal verbs do.
In French all modal verbs belong to the group ending in
-oir belong to this group. And, if this wasn't enough, all modal verbs are irregular. Since these verbs are going to be used very often, you should know them soon.