There are many threads like this up already. Check the catalog folks.
>>240493
>>240623
I highly suggest you go to /fit/ and ask this. You may say "ew but I don't want to be a bulky manly Arnold Schwarzenegger". I'm far from a gym expert but I do know that's not how exercise works at all.
Everything I'll say is anecdotal. I'm happy with my results but you might experience it differently, so do your own research outside this stupid board. In order to gain weight eat balanced healthy meals with plenty of proteins and carbs (extra emphasis on the proteins). Do not snack a whole lot in between meals and do not eat junk foods all the time. It is ok to take cheat days but don't do it too often. If you have trouble eating more, a regular workout routine helps a lot with kick starting your hunger. After workouts your body needs energy to recharge and rebuild itself so eating plenty is key. Also only drink water, tea and unsweetened coffee.
As for workouts do cardio, light lifting, yoga, etc. Look up exercises for women, they are low impact and tone up all the same muscles in a male's body. Do this 3-4 times a week. If you think you're becoming "too manly", you can cut down the intensity of your workout, but please do not stop it all together.
As for ass workouts, do your squats, deadlifts, donkey kicks, lunges, running, cycling, etc. All the time I see anons on this board thinking that round jiggly asses are like that because of fat. Unless you have unusual genes like assbro, this is not true. A nice ass is nearly all muscle and takes lots of workouts to get it to build up that muscle mass. On top of that it also comes down to straight genetics.