creating and importing new brushes

I'm sure many of you have done it, gone onto a photoshop, etc brush site and helped yourself to the brushes they have there. what i would like to do is start experimenting and creating my own brushes. Though i have no idea about how to go about it, is it a simple case of changing the file extension to .ABR or is there more too it? (i think theres more to it, because the brushes i have downloaded usually have more then one brush per pack)

thanks in advance ~ Chapel

It's really very simple. All you do is use your marquee tool to select the area you want to be a brush. Then go to edit>define brush. Give it a name and there you are. If you want to make a set you'll have to compile all of them together and then go "make set" or something but you'll figure it out. Good luck.

tom