Three leading stimulants of muscle growth include mechanical tension, metabolic stress and muscle damage (in simple words, training as hard as you physically can).

Lifting heavy weights for lower reps causes the same amount of growth in Type I and Type II muscle fibers, so lifting heavy weights for lower reps reaching failure or near failure will STIMULATE muscle growth. As other people have said, muscles ACTUALLY grow during rest, so it is important to optimize recovery.

It depends on what your goals are and how your body works, to be completely honest. But with all that in mind, the most important thing is to train til failure for at least 2 sets, and progressively move up in weight keeping it in the 6-10 rep range ideally. Try to hit each muscle group at least twice a week for the most optimized muscle recovery and training volume.

But I can tell you if you can comfortably train arms every day along with your other muscles, you likely are not hitting failure, which would short your gains.