What type of area do you live in (urban, suburban, rural)? Are there trees in the park? Then do the pull-ups/chin-ups from a tree branch. You can do dips between two sturdy chairs, between two counter tops (either between an island and another counter top, or where two counter tops come together to form a right angle), between where two railings meet (on a porch, fire escape, etc...). Really you just need to use your imagination.
Or alternatively you could invest in a set of gymnastics rings. They're not free, but they will allow you to do a large variety of exercises. Here is the type that I myself have. They are adjustable (to different heights), so they allow for easy changing of exercises.
Finally you could potentially invest in a free weight set. It's also not going to be "cheap", but it will be well worth the money if you actually use it.
But at under 16 years of age (which I am assuming that you are from a previous statement that you made), just about anything is going to be beneficial for you.
Good luck and good training,