Why do leaks occur?.

As vehicles age the seals breakdown and this causes fluid to leak out. If these leaks are not dealt with and the fluid levels not checked then the Transmission will fail.
Overheating of the transmission caused by pulling heavy loads can also destroy the seals.

Identify Leak

Transmission fluid is usually red or brown in color. To be able to identify if it is the transmission leaking you will need to locate your transmission.
The Transmssion will be attached to the engine and will either be at the side or behind. If you see fluid on the transmission or on the ground underneath then you probably have a leak.

Check Transmission Levels

Drive the vehicle for about 20 mins to warm up the transmission fluid and then park it on a level area (Not a hill). Using the parking brake and foot brake (To stop the vehicle moving) go through the gears with the selector and then put it in park and pop open the hood. Pull out the transmission dipstick, wipe the end with a rag, put it back in then pull it out again and read the level.

How To Stop Leak?

For small leaks you might be able to use a Stop Leak oil designed for your car and transmission but be careful to get the right one as some will block the internal filters of your transmission which will take it from a leak repair to a transmission rebuild. Also do not add more fluid that is required in your transmission.