I'm just glad you didn't choose ubuntu. IMHO, you don't really learn anything with ubuntu. Although, I am rather surprised and commend you for choosing slack.
-God Ginrai
That depends on what you do. To really learn Linux one must use it. If ubuntu makes it easier to do your day-to-day tasks in Linux and allows you to make the switch then learning and experimenting will automatically follow.
The best way to learn Linux is to immerse oneself. That is, only install Linux on all of your computers and ditch Windows altogether. This forces you to deal with whatever problem crops up. I personally recommend ubuntu for its wealth of packages and good community.
After this you will gradually start to customize things and grow into the more advanced stuff. Don't jump directly into Linux from scratch. It's a great way to learn stuff, but it forces the beginner to deal with too many things at a time.