Where do you put transmission fluid in a 1996 Geo Metro?

If it is an automatic you will likely have to add fluid through the dipstick tube. This is a real pain because the diameter of the tube is quite small and overflows easily. You will need to buy a funnel where the size is very close to the inside diameter of the upper neck of the tube. It will still probably make a mess though. It helps alot if you heat up the fluid before adding it, lowering the viscosity keeps it from overflowing in the tube.