Mashou is used after the base 2 form of the verb - to say ‘let’s do something’ e.g. tabemashou = let’s eat. It can also be used to say “I’ll do…”
Kuru means “to come” - the base form is ki. So polite present form would be kimasu (will come) , polite present negative tense, kimasen (will not come), kimashita past tense (came), kimasen deshita past tense negative (didn’t come).
Suru means “to do” - it can also turn nouns into verbs. It goes after the noun, and turns it into a verb doing action, as opposed to a static thing e.g. benkyou suru (study). Base form is shi. Polite present shimasu (do) e.g. watashi wa shimasu (I will do), shimasen (won’t do), etc.