It's not open source but for your purposes of figuring out if audio editing is for you Reaper could be a nice introduction. It runs on Linux and works pretty similar to most commercial DAWs. You can run its evaluation mode for free indefinitely with a nag screen at startup. I started with that and then graduated to Cubase when I decided I wanted to pursue further.
REAPER runs really very well on Linux, it has to be stated, and is one of the easier DAW's to learn thanks to things like "The REAPER Blog" and "RAPER MANIA" channels on Youtube that really make REAPER great. It is one of the best values for money in the DAW world as well. VERY, very powerful software, great price.
