Here’s an article on how to have group sex (although there are no universal rules, and it’s best to just check in with everyone involved). Group sex can also happen at sex parties, which have more defined rules and norms. Here’s a guide to help you navigate (gay) sex parties: part one and part two.
Having sex with multiple partners means it’s especially important to use protection with each partner. Condoms and other barrier methods are easy to use and available! Check this out for a whole safer sex tool box, or check out the safer sex resources page.