A word of caution, you must install the RAM Apple specified for your system. Be sure to check out the technical information manual that shipped with your computer. Also, the Mac community has experts like the Gurus to turn to when you need help. Another consideration is the type of RAM in your system. Some Macs also support memory interleaving.
Memory interleaving doubles the data path through which data flows.
In the reference system, a PowerMac 8600, the memory controller has a 64-bit data path. When RAM chips are installed in identical pairs in matching slots, that data path widens to 128 bits. In the picture below, the RAM slots marked with an asterisk indicate memory interleaving. Most of these systems are still limited to the 50Mhz system bus speeds, but there is some benefit to this wider data path as Apple has repeatedly pointed out in its marketing of the G4 line. As you can see from the picture, OS9 alone is using over 50 MB of the 224 MB installed on my machine.