How do you start finding clients for freelancing? How do you figure out a competitive rate without going too high or low? I have about 10-15 hours of real work

How do you start finding clients for freelancing? How do you figure out a competitive rate without going too high or low? I have about 10-15 hours of real work to do each week at MegaCorp. The rest is idle time at my desk/couch. Thought about moonlighting and doing 2 jobs but freelance sounds better.