Clench that butt !!

Hi and good luck on your weight loss journey. Butt clinching alone will not do much for you - it will activate your glute (butt) muscles but you need to do much more that just activation to tone a muscle. To tone and shape your butt and thighs you need to move - you also need to burn the fat that sits under the skin (subcutaneous fat) to achieve a toned look. To do this you need to do things like lunges, squats etc (for toning) - standing weight bearing exercises are always better and more functional than those lying in the floor. To burn the fat you need to do aerobic exercise - this could be anything that raises your heartrate, and leaves you feeling hotter and having to breath more deeply, and developing a bit of a sweat - anything from walking briskly, cycling through to Aerobics, Cardio type classes will do the job.

As you tone your legs doing squats, lunges etc this will also help you gain some lean muscle tissue - which will in turn help your weight loss efforts as it is muscle which metabolises.
Good luck