This is my first attempt to use Audacity. I have a simple request. I have six mp3 files which I need to merge into one. What do I have to do? 
Adalbert
I assume you want to join them one after another, not mix them so they play at once?
[u]Here[/u] are some instructions.
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About MP3 -
As you may know, MP3 is lossy compression. When you open an MP3 in Audacity or any “regular” audio editor it gets decompressed. If you re-export as MP3 you are going through another generation of lossy compression and some “damage” accumulates. You may not hear any degradation but it’s something you should be aware of. If you want MP3 or another lossy format It’s best to compress ONCE as the last step. Or if you have an MP3 original try to minimize the number of times it’s re-compressed. (The loss happens when the file is compressed to make it smaller. There is no additional loss when it’s decompressed… and it’s getting decompressed as you play it anyway.)
There is a (free) special-purpose program called [u]mp3DirectCut[/u] that can cut, join, and do some other limited editing without decompressing.