To upload your comics to Keenspace, you need to FTP them to the Keenspac Server.
FTP stands for File Transfer Protocol. In non tech jargon, A FTP client is a program that brings the files from your computer to Keenspace's computer. There are plenty of free ones out there, so do a search on Google. Or if you know of a good free one, post here and let me know so I can link it up.
Edit: LennyZ posted a thread that listed a few good sites which I will include here. Thanks Lenny!
SmartFTP - Popular favourite, seems to used by the majority of people I know.
FireZilla - Never tried it, but I've been told it's good for beginners
WS_FTP - Heard that it's simple (and therefore also good for beginners)
LeechFTP - Been told it can handle multiple transfers at once.
RBrowserLite - A pretty good Mac OS X ftp client for beginners. Nothing fancy, but it just works. ;)
Different FTP Clients have different user interfaces, so it's impossible for me to cover them here, but FTP Planet and WEbmonkey have FTP tutorials which should help. Google for FTP tutorials for your particular client if you have to.
Internet Explorer can also be used as an FTP Client.