What's the science on working with your own body weight? (Jumping jacks, lunges, push ups and all that other fun stuff)

I know its working for me cuz I see changes but how often should I do it.

Either do machines, body weight and/or running, 5/6 times a week and trying to figure out a good balance. Probably gonna add swimming too.

Not trying to be a beast or anything. I just like to be fit and the gf doesn't mind either.