Refrigerators with a defrost cycle drain the melted water from the evaporator coils through a tube or a hole into a drip pan underneath the refrigerator. The water usually evaporates, but most times the pan is removable and can be drained. If this path of water is blocked at any point because the drain hole or tube is crimped or clotted with anything, it will back up inside the refrigerator area and try to find a way out, usually under the crisper drawers. To fix this, clear the obstruction in the drain tube. The drain pan at the bottom of the refrigerator can overflow or get old, crack, and develop a leak. Other times, mold can grow in the drain tube and clog it.
Most refrigerators have an ice and/or water system built into them. This means that you have a waterline attached to the back of your refrigerator and it comes out as ice or cold water. Anywhere that water travels through the refrigerator and freezer can turn into a leak. To find the leak, you need to follow the tubes that carry the water through the appliance and make sure that all connections are tight.
Leaking containers or spills in the refrigerator can be misdiagnosed as leaks. First make sure that there are no puddles of juice, milk, water, etc. on one of the large capacity shelves.