about have to, must and had to

English as a Second Language English Vocabulary, Grammar and Idioms
1

Dear Torsten,

thanks for lesson 5; So can you explain,when I can use" have to" ," must "and “had”.
I all confound its, excuse-me if my sentenses are wrong.
I will hope receive your respons in short time and the lesson 6! THANKS.

All best for you.

Raharison