Obligation and necessity

when the speaker feels that an action is necessary: I must call my brother today. (he is ecpecting my phone call)

by someone in authority, e.g parent, boss,teacher : You must hand in your assignment by Tuesday.

in writte rules, instructions :All accidents must be reported to the police

when an action is necessary, because someone else requires it or because it is a rule or law.: You have to wear school uniforms in this school

for habits : I have to catch the bus to work every day

Use don't have to when there is no obligation to do something.: You do not have to wait

we use needn't and don't need to talk about lack of necessity in the present or future.: You needn't come or you don't need to come to the party. (if you do not want to)

Don't have to and don't need to are similiar and you can choose which one to use