The refind-bin file contains rEFInd binaries for use on an EFI System
The refind-cd file contains a bootable CD image file; burn it to an optical
disc and you should be able to boot rEFInd to test it without installing it
on your hard disk. This image is more likely to work on PCs than on Macs;
at least on some early Intel-based Macs, the CD boot process has special
requirements that this image doesn't meet.
The refind-src file contains the source code to rEFInd, which you can build