to check or change your tranny fluid the process is a bit like your diff. there are two bolts, one on the bottom for draining, and one on the side for filling and checking. what you do is drain your old fluid, than replace the plug. than using a pump system or if you find a long enough hose (you need to use gravity to get the fluid in) you need to fill until the fluid just starts to spill out (ever so slightly).... to check the level you need to open your side plug and if a bit drips out than your safe, if not stick your finger in , if you can feel the level is just at the edge than it will be ok, if its a bit lower than you can top it off.
auto tranny fluid is suppose to be lifetime (although i dont buy that) manual tranny fluid i change every season, just because of the way i drive , its a bit excessive but it cant hurt