Is it possible to catch an STI during oral. I’m bisexual, does that work for both genders by the way?

Yes and yes

What are you supposed to do to prevent it

Yes it is possible. To prevent it you can use barrier methods like condoms, female condoms or dental dams

Yes to both. Use barrier methods or if you’re exclusive with someone be sure to get tested beforehand.

Everything said above and get tested regularly and ask your partners if they have been tested