iPhone 4s leaking weird substance, has 2 small shadow bumps on the side of screen, and is getting hot very quickly

Internal pressure is almost certainly a safety issue and battery failure mode. Same for anything leaking out. Even if the substance entered the phone and not something decomposing from the materials made into the phone, you don't want electrical shorts or anything leaving the case of an iPhone.

Think potential fire hazard if the battery is swelling or leaking and get the hardware to someone that is qualified to diagnose a failing battery and physical damage. Call Apple if you can't take it to someone for service. 1-800-APL-CARE

Do not charge it or connect to any USB - I would power it off immediately from the description you have listed.

You can also get safety information from: http://www.apple.com/us/search/iphone-safety?find=iphone+safety and select Support to narrow the results to specific hardware safety and manual download instructions.

Once you have some guidance, you might power it on one more time to perform a backup if you don't have a recent one. Again, don't leave it unattended until you're sure it's stable and working correctly. If you can't get it cooled, consider calling for help - local fire department if needed.