very easy. boot your pc into windows. open my computer or windows explorer (do not open ezcdcreator). double click on the iso file. EZcdcreator will open and prompt you to click "go" or whatever to start a disk burn. put a blank disk in and start the burn - easy as that.
btw... iso files are a pre made, burnable "snapshots" of a whole cd, saved as a single file, made specifically for cd burning programs. they take the cd data and all the burn settings (such as bootable etc) and encapsulate them in a single file. they are made so that you can just download the file and not have to know any specifics (which files to include, whether to make the disk bootable, etc) its is all taken care of for you.