Overfading two tracks

I’m a novice in using sound editors, not even familiar with the termonolgy used. But I want to make one track out of two. And the first track must fade out while the second fades in.
Can anyone help me out?

The basic technique is to have the two tracks one above the other so that they overlap where you want to “crossfade”. Then apply “Fade In” and “Fade Out” effects to each of the overlapping regions. When you export to create a new audio file, the tracks are automatically mixed together to produce a single file.
There is additional information in the manual.

The next release of Audacity (2.1) will include a new “Crossfade Tracks” effect that makes the task easier.