1990 Chevy Lumina Leak?

[Blake E]

I've got a 1990 Chevy Lumina Euro 3.1l and today I pulled it in my garage and backed it out and noticed antifreeze on the ground, I just replaced the radiator with one from pull apart and checked the anti freeze in it and it was full except my over flow which every time I put antifreeze in it, it goes empty but I can never tell were its leaking from can anyone tell me some places to check to see were its leaking? Also my low coolant level lights on but the antifreeze in the radiator is fine