Welcome to FT!

You will claim your baggage and clear customs in TBIT. Then you will recheck your bags for your domestic flight in T7. You can walk around from TBIT or take the airport terminal bus. LAX is shaped like a horseshoe with TBIT at the "bottom" of the U shape and T7 at the "upper" right. I don't think (and someone please correct me if I am wrong) that there is a way to check your bags for your UA flight at TBIT.

LAX is pretty well signed, so you should not have trouble finding the baggage claim on the lower level. One note though. All departures at LAX are on the upper level, baggage claim and arrivals are on the lower level. After getting your boarding pass at the UA ticket counter or kiosks you will need to go back upstairs for your domestic departure.

Again, this information will be readily available at the airport and from the staff there.

Have a good trip.