YOu use a kitchen to make a ROM.
Check out
http://ppckitchen.org/ it is very user friendly, I have used to build cricKet ROM's for almost a Yr now. It lets you build alot of different ways. IE: wm 6.1 or wm 6.5 operating systems. Programs and setting you want don't want. Take a look at it. There are alot of others out there download one and start playing with it, that's how I started.
To use some of the others you just need to read up and follow the threads that they are in.