2 exercises is all you need:
1. Push ups - Start on your knees, do as many as you can. Work your way up to regular push ups, then to make it harder you can try with your feet on a book or chair or something. I find a good way to do these if you make a plan where whenever you walk into a certain room you decide to do 10 push ups every time. This method works really well!!
2. Squats - just using your body weight, feet hip distance apart and arms straight out in front of you, bend your knees without letting your knee's go in front of your toes, sticking your butt back, and try to keep your body weight in your heels. Do them everyday and increase the number as your endurance increases.