It's an expression to say that where we are now, in here, is safe and that outside (out there) is like a jungle - wild animals, no map, dangerous terrain. "Good luck in your new job - it's a jungle out there!" = your new job will not be easy, like exploring thick and dangerous jungle. Be careful.

If you got this from the song "It's a Jungle out There" by Randy Newman, This simply means that disorder and confusion exist in the world. The song lyrics answer your question... "Disorder and confusion everywhere | No one seems to care...Poison in the very air we breathe"

It's a jungle out there= the laws of the jungle apply= only the strongest will survive

What context is this from? It really depends on where you heard this statement.