Desert temples can only be generated in the desert biomes, so you simply need to find them in the desert biomes. First go to find a desert. Once you find a desert, you can begin searching for a desert temple.
There is a small chance of finding one with each individual desert biome. You have to wait and wander in the desert. Eventually you should be able to find one.
You can go inside it. The floor of the desert temple will always generate at Y=64. This is the reason you might often find the desert temples buried in the sand.
There are four loot chests in each desert temple as well as a TNT trap. Dig a block on the floor and go down at the bottom in the tunnel to get four chest boxes and a TNT trap door from there.
Goodies found from four chest boxes can be seen below: