gravity fill is the best and cheapest way, the draw back is a long time.
The other way is the bleeder valve located near the belt on the valve cover. theres a small hose running from that to the reservior. With the engine running fill the reservior up, and open the valve, there should be coolant coming out once the eninge starts warming up. continue to monitor the temp and add coolant as necessary. If the stream coming out is solid ie.. no spurt but continuous, then the system has been bled. Be careful since the engine is running, do not wear loose fitting clothes and use a socket, you can use a wrench but the fluid is hot when the stream is continous, if you drop a tool and the belt catches it, you may have to replace the belt and/or pulley(s).
The safest and most reliable way is to create a vacuum in the system using that same valve and suck in the fluid, this may take 1 hour but its the safest way.