For the time being, we’re not worrying about 1/2 cover, but we’re calculating 3/4 cover as written. Basically, you can hide behind physical objects pretty much normally, but hiding behind creatures won’t work.
A short rest takes ten minutes.
During a long rest, you recover abilities, spells, and 1/2 your hit dice as normal, but you don’t automatically recover hit points. You may spend any number of your hit dice, before or after having recovered them, as per a short rest.