77 year old female 6 months out of back surgery

My doc said I could resume exercise. I need to BURN FAT and BUILD MUSCLE! I am flexible and able to bend, touch toes (properly),and walk on treadmill, but my endurance has sadly been horribly reduced. I have started walking, doing some T-Tapp and other exercises, along with some exercises provided by the PT. Please give me your best suggestions as to how I might incorporate your Tabata Training into my exercise program and accomplish, more endurance while burning fat and building muscle! Thanks!