Just got a non immigrant B for the first time. It is a multiple entry. I used to have a non immigrant O, and know how that works (had to leave every 3 months and get a visa stamp). I have no idea how this non imm B works.

How often do I have to leave, if at all?

Should I carry anything with me, such as invitation letter from a business, etc?

Anything else I should know?

Thanks.

It works the same. You can only stay for 90 days at a time.

It works the same. You can only stay for 90 days at a time....

Sorry disagree with you..depends what it is tied to ie work permit...if you are doing 90 day reporting you dont need

to leave the country...

A Non Imm Visa Multy Entry only gives 90 day stays at a time.

There is no 90 day reporting on a visa entry - it allows the same 90 day entry as a non immigrant O visa. Only if you are on a one year extension of stay you do not need to leave the country - on a visa entry you do.