hey Vic - you must remove those gears in order to get at the holes in the rim on the drive side.
1) take off the wheel
2) look at the inner area just between the smallest gear and the axle of the wheel. You will see one of a number of things which will reveal to you what sort of tool you need ( called a freewheel removal tool ) to get that thing off.
3) go to the bike shop and buy the correct freewheel removal tool or tell the guy you have 3 bucks if he can pop that freewheel off for you.
4) if you get the tool, note that it has a hole in the center. remove the quickrelease (QR), thread its axle through the hole in the tool, press the tool into place on the wheel and tighten the QR until it holds the tool tight to the freewheel.
5) get a big wrench
6) with the wheel clamped between your legs, drive side on your right, wrench in the reverse direction that the wheel spins when you are riding it. This can be really, really tough if it has been on there a while.
7) use a little light duty grease when you put the freewheel back on. The action of the chain will tighten it as you ride it, no need to wrench it back on.