hotlinking / htaccess question

I do websites for my friends because I can use FTP and I like to play with Dreamweaver.  This does not make me a "real" webmistress by any means.  Unfortunately, someone (or several someones) from that Russian bulletin board are hotlinking to a ton of images from Dana's webspace.  Can someone please tell me wtf htaccess is, and how one might use it?  I know nothing about server-side stuff, though I do know that everyone I help is on Apache servers (as am I).

Also, there seems to be some indication that htaccess would then make it impossible for people to use the LJ graphics stored on their webspace, though I'm not sure why... If that is the case, though, then it won't work for us, and I'll just have to rename all the files.  Feh.  But that  I know how to do.

If there are some online resources about htaccess (and other Apache commands) that someone could point me to, I'd really appreciate it. 

And now I'm going to go get vehicle emissions testing done and stand in lines.