You do not need a gym to build strength and muscle. With a pair of dumbbells, a pull-up bar or just your bodyweight you can get a very long way. What counts is exactly the same as in the gym: make the exercises harder over time.
Key principles
1You can add load with bodyweight too: more reps, harder variations or a slower tempo are all forms of progression
2A pair of dumbbells and a pull-up bar are the two best investments for home training — cheap and extremely versatile
3Upper-body pressing: push-ups, dips between two chairs and dumbbell overhead press cover chest, shoulders and triceps well
4Pulling is the hard part without equipment — a pull-up bar is close to essential for training your back properly at home
5Leg work translates well to home: squats, lunges, hip thrusts against the sofa and Bulgarian split squats build real leg strength
6Planks and core work need no equipment at all and build the foundational strength that helps every other lift
Example weekly plan
MondayUpper body push (push-ups, overhead press, dips)
WednesdayLegs + Glutes (squats, lunges, hip thrust)