Hi

I am 16 years old, and want to know which is the best way to do push ups, I know there is many variations, such as inclined, on knuckles etc

Which is the best for building up biceps and chest?

Thanks

The classic one is classic for a reason, it works the big muscles best. You can vary it by putting your feet on a chair or your hands on a stair to alter the angle you hit your chest muscles (like doing incline or decline bench press). Bringing your hands closer to your chest works the triceps harder.