i personally would avoid the use of rom manager,with exception of using it to flash clockwork recovery(i wouldnt use it for that either,but if your new its an acceptable way to glash it).
rom manager is an app,in a working rom,and therefore will not always be available to you. if youre hung in a boot loop or non-functional rom,you will have no choice but to use your custom recovery and do it manually.
revolutionary may have installed it for you. you can enter recovery several ways: thru hboot,thru rom manage,or thru an app such as quickboot. most custom roms have an option to boot to recovery from the "power off" menu.
once youre in recovery(usually clockwork,but there are others) use the menus to make a nandroid backup, wipe data,cache,and dalvik cache and flash your rom.
*always make a backup!*
check out the root sticky. alot of the guides link to a thread called "[how to] and some root terminology".
read thru the terms,and the guides in that thread,and that will give you a good start on the knowledge you need to be a successful root/rom-er.
just post if you have any other questions after checkin out all the info.