I need to know how to have a three sum with one female and two males

And am only 20 yrs old

What is it that you need to know? First you set up rules and everyone agrees to them. Next, you find two other people.

You can always look at porn sites or sex ed sites to master your technique.

Or you can search AMHD and see what other people have posted.

Not the least of which is deciding who gets to be airtight... you or her, or both of you.

These days VERY recent test results for any STD would be a precursor to everyone even being considered. And that's even with condoms all the way around.

WHY do you want to do this? Your reasons have an impact on my answer