A green pool requires a good dosing of Algacide. This chemical can be purchased at any pool or spa center and it takes very little time to clear up the green. Change your pool filter or give it a good cleaning to keep the algae from coming back.
You have too much algae and not enough chlorine or other purifier disributed through your water. Check the instructions for your pool for doing a "shock" treatment - and plan on giving the plaster and tiles a good scrub once the water is clean again. Don't forget to clean out your filters, or the algae may bloom again.
Use algeacide ( which can generally be found at any store that sells pool chemicals)and make sure you use your pool test kit and the water has the right amounts of chlorine, and the PH levels are correct.