I downloaded audacity last week to create a continuous medley of several different songs. I finally figured out how to create the mix so each track plays back to back. After listening to the exported mp3 everything came out fine BUT some songs were louder or softer than others and it really ruined the whole mix. i know there has to be a way to make sure each track has the same volume so it sounds even. I read about amplify and normalization in the online manual but it honestly just confused me lol. I would really appreciate it if anyone could tell me how to fix this 
You might find Chris’s Compressor useful.
http://theaudacitytopodcast.com/chriss-dynamic-compressor-plugin-for-audacity/
Chris designed this tool to even out opera volume variations so he could listen in the car.
If it gets close but not enough, change the first setting, Compression from 0.5 to 0.77.
That the setting I use for podcasts.
Koz
Put your whole mix on the timeline and apply Chris to the whole thing.
The whole show is going to change. Play enough of it to make sure the songs more or less match.
Koz