Did you drive it when it was out of coolent?, if so, you could have harmed the engine, if not, you are so lucky. If the leak isn't a big one, you might be able to pour some antifreeze in to the radiator (fill it to the top)...you have to push down and twist counter-clockwise on the cap to remove it. NOTE The white plastic overflow tank is not the radiator !!!
Then you might be able to drive it a short distance to a shop for repairs. If the leak is big, ( busted hose, ect...) it might be best to have it carried to a shop.
Caution, it you drove it without coolent, and it got "hot", you could have damaged it (the engine) to where it might cost more to fix it than it's worth. So, you might fix the leak, only to find the engine is "broke" too. Knowing this before hand might help you decide how much money you want...need to spend to fix it right. I would suggest you talk with Dad, or boyfriend. Good luck