Congrats on moving to a Mac. Hope you enjoy it. I moved over the summer, and it's been great.
For real newbie type questions, you might also want to check out the Apple user support forums at discussion.apple.com
While you are a newbie to Mac, are you a newbie to video and or digital photography?
If you are truly a newbie, then I recommend first exploring iPhoto and iMovie, and see if that works for you. Can can see tutorials for both on
http://www.apple.com/ilife/tutorials/ The iLife suite is generally very useable and helpful to novices. In general, though, you might need to make a mental shift from the PC. In PC-land, you may be used to managing your own files yourself, and then pointing applications at those files. In Mac-land (at least, iLife land), you load your content into iPhoto, iMovie and iTunes, and let those applications manage the data for you. You literally put your content into the application database, and you stop messing around with your own file structures.
If you need more help than this, it would be useful if you explained a bit more what you are trying to do. When you say you "use GIMP to compress your photos" -- what exactly do you mean? Are you shooting in RAW and compressing to jpg? If you are shooting in jpg, then I'm not sure what you are doing to "compress" the photos.
Same goes for video. What format are you capturing in, and what do you mean you are "compressing" your video files? For instance, I have a bunch of old DV tape off a Sony DV camera that, when captured, were converted into avi files. I used Quick Time pro to compress them into h264-based mov. There are many other tools reportedly better than QT that you can use, as well (iSquint, VisualHub). Generally, this is referred to as "transcoding" and the result many (most) times includes compression.
If you'd like more specific responses, I suggest specifics on your equipment and output. For instance, I use a Canon ELPH SD800 to shoot some videos, which puts out MJPEG AVIs that iMovie easily ingests. Other formats it may not so easily work with. So, details are very helpful, if you desire helpful responses
If you are unsure of the formats you capture in, then at least specify the equipment you use, and what you are trying to achieve, if anything other than compression (which is simply making a larger file smaller). If you are just trying to compress files to save space, then perhaps just a zip or archive solution would work just as well.
