workouts to gain muscle

Hey guys! I'm really skinny & have a fast metabolism. I used to workout & my body actually gained some muscle but I had undergone foot surgery so had to stay immobilized for some time & let's just say I deflated lol. Do you guys recommend any workouts to gain? Especially workouts that focus on the glutes** also, should I follow a certain diet? 
Alsoo, how do I keep myself motivated? That's always been a problem for me to continue 🙄