Hostile environment usually refers to sexual harassment of some kind, or jokes, conduct, comments, that are offensive and that make it more difficult for you to perform your job.
Hostile environment could also be harassment for other reasons, for example, race, sex, age, disability. Generally hostile environment, though, refers to a hostile sexual environment because of jokes and comments that are unwelcome.
The first thing you should do is tell whoever is causing the problem to stop, and then you should also report that conduct to a supervisor. Check your employee manual and see who you should report to if you are suffering from or experiencing sexual harassment or a hostile environment in any form.
If that doesn’t work, then certainly you should contact an employment lawyer.