Well for a start it actually checks the sum of the file against the one entered by the user or searches the given sumfile for the sum of the program you're checking and outputs both sums and if they matched. It also saves any locations you used previously so you don't have to retype them. The sumfile can be located on a server and downloaded via ftp or http for example if you get a file from ftp.slackware.hu via linuxpackages.net you can use
ftp://ftp.slackware.hu/linuxpackages.../CHECKSUMS.md5 and that will be searched to find the checksum. I hope this is clear enough homey, if you have any other questions feel free to post 'em.
Cheers.
Adam