What is the difference between come stai and come va ?Feel free to just provide example sentences.

yes it matters because if you speak to someone informally you use either "come va?" and "come stai?"

I would not use come va? in a formal situation but now I am explaining you how to say how are you in a formal situation

when you talk to someone formally, like your boss, or a university professor, someone you deserve respect, someone you don't know in general (usually except for children and very young girls or boys), you use the question "Come STA?"
when you refer to a person like the ones I described before you usually talk to them not using the second singular person (TU), but using the third singular person in this way: LEI
And you never say CIAO to these people, but you use formal regards like BUONGIORNO during the day
BUONASERA in the evening
SALVE in either cases

example of conversation; you are A and meet a university professor (B) to the mall:

A: Buongiorno professore

B: Buongiorno A. Come STA?
{pay attention to the word "sta". If you were in an informal situation you would have said come STAI.}

A: Bene, grazie; e LEI come STA?
{so in formal situations you use the third singular female person. in this sentence LEI refers to the professor and in English you would use You; either STA refers to the professor and in English you would use Are}

This may seem a little complicated but it is totally learnable with practice!