If it's your roof that's leaking you need some-one to get up there to check for loose, missing, or broken tiles.
Pray that it's just a loose one that can be tapped back into place, as the proper way to replace missing or broken tiles involves removing the tiles and then replacing them again, which usually means getting the experts in as this can be a dangerous venture, depending on the height of your house. It's a long way to fall from two storeys high