Can I lose weight and grow muscle without going to the gym or without using weights?
Absolutely, by doing Calisthenics.
Calisthenics is bodyweight movements that require only a pull up bar to perform.
Among these exercises are:
pull ups, chin ups, push ups, dips, leg raises, side planks, supermans, squats, and calf raises
These are the most basic and can get you far just by themselves.
Do them all in a circuit, repeat it three times in a workout, and do that workout 3-4 times a week.
This will get you taken care of workout-wise, but there's another element.
Diet is the most important for losing weight and growing muscle, so you'll want to get a good diet as fast as possible.
This means, no sugar, much less carbs, much more protein, much more vegetables, and a caloric deficit.
If you keep your calories low and eat the proper foods, you'll begin losing weight rapidly, especially if you're doing calisthenics with it.
I go over all of this in much more detail my FREE 7-part beginner calisthenics guide. It will teach you everything you need to know to get started with calisthenics and begin working towards a functional, athletic body.
Best of luck,