We have this microwave in our camper. Try pushing Timed Cook first, followed by the amount of time you want it to cook, then Start. This will cook the food on high.
If you want a power setting less than high, push Timed Cook first, followed by the amount of time you want. Then push Power, followed by the power number you want, then Start.
Hope this helps. I will say that this microwave is much weaker than the one we have at home, so you'll have to experiment with the settings to get something to cook the way you're used to.