we use "must" for an obligation. when you oblige someone to do something you must use "must" or you use "have to" to show obligation ( you must do)
"have to" is the base form of "must"
we use "allowed to" or "can" to express possibility (as you like you can do or not)
we have many terms to express contrast like : however , whereas , but , although, despite of , in spite of
contrast means to talk about two things in one sentence
comparative means to compare between two things
you use more or less with long adjectives
the adjective + er when we use short adjectives
