How to use hopper gun to apply drywall mud to walls in rental mobile home
Texture isn't terribly hard, but there's a few things to note. 

Last question first: texture isn't going to hide much in the way of damaged drywall unless you really lard it on. Fix the drywall first.

You'll be shooting texture, not drywall mud. (Texture is usually sold in powdered form and mixed by you. Practice mixing/shooting.) 

Check that your air compressor puts out the required CFM to run the gun. (The hopper gun will specify.) You might need to rent a bigger compressor.

One coat is usually the right number, but if you really screw up and have bare spots, you might have to let everything dry and shoot more on top. That's hard to do well, so don't mess up. (If you put too much texture on, just trowel it off when it's wet and shoot again. Obviously, this isn't an option if you're on the second coat, so it's extra stressful.)

Decide in advance what kind of texture you want (orangepeel, knockdown, etc) and practice on some scrap. (Different nozzles/pressure/speed give different patterns.)

You need to mask off everything you don't want texture on. This might be the most tedious part of the job.

It's nice to have a helper that can dump the texture mix in while you hold the hopper.

Did I mention practice? You should practice.