Please refer to this page for posting code on the forums: Using code tags properly
As for a double jump, try adding a variable ‘doubleJump’. Now, if you’re not grounded, and you’ve jumped, but not double jumped, check for jump input and allow another if you get the jump button, and set double jump to true.
Reset double jump to false when you hit the ground.
If you’re very new, I’d highly recommend that you begin with some introduction tutorials from the Learn section: Learn
I’d suggest doing some tutorials for “Unity interface & Essentials”, “Scripting”, as well as at least 1 or 2 tutorials (Roll-A-Ball, Space Shooter), and continue from there. They will help you a lot going forward.
Good luck 