Sac spiders are small (up to 1/4 inch long), brown, and have a sac-like structure on their abdomen. They are most easily identified by their small size and their sac-like structure.
The best way to get rid of sac spiders is to eliminate their food sources by thoroughly cleaning your kitchen and bathroom. You can also use commercial fly traps or bait. If you have a severe infestation, you may need to call a professional exterminator.