Just add fluid to the coolant reservoir till it's at the full line....start the engine and let it run....if the level drops out of sight add a bit more...once the electric fan comes on it's at full temperature and should be at the normal full line on the reservoir tank. You can do all this with the reservoir cap off as it is not a sealed system. The reservoir tank is the plastic bottle on the left side of the motor under the plastic fascia.
If you just put the radiator in and has none in it, yes the cap is on the right side next to the neck. Fill it to the top. Start the bike and while its running watch the reservoir. you may have to add to the upper line.
the proper way to do this is called "burping" the system. with the pressure cap off start up the bike and let it warm up to the point you see the coolant moving in the filler neck. blip the throttle to spin up the water pump and burp out the air. you do need to do this several times but you don't need to red line the rpm when blipping the throttle just up to maybe three grand. after that let it cool overnight and top off the filler neck and the overflow bottle, done. some of my kawasaki's had what looked like a brake bleed nipple right next to the filler cap and you could loosen it while you filled the system to reduce the chance of air pockets and you could bleed it off once hot and pressurized too just watch out for hot coolant, put a hose on it and run it into a bottle. :bigthumbsup: