There is a drain plug on the bottom of the tranny and a filler plug on the side of it. When you fill up the tranny, the fluid level should be right at the bottom of the filler hole, where you can just stick you finger in there to check for tranny fluid.

A rule of thumb for changing tranny fluid is at every 24k miles or 2 years which ever comes first. But the only way to know for sure when to change it is by the recommended interval the manufacturer says to change it at.