How to customize crop ratio

I thought its a breeze to customize my own crop ratio but appears not. There is nothing under Help and just browsed thru' some books in the library also didn't cover this area.

One eg. of the default setting is “crop 4 inch x 6 inch 300 ppi”. I want to customise a square crop format, so I type 2 version following word for word “crop 6 inch x 6 inch” and “crop 6 inch x 6 inch 300 ppi” and saved tool preset. Both version didn't work.

Have I missed something? Would appreciate if you can show me the steps where I've gone wrong. I'm using CS5.

Thanks
David