Press F5 on your keyboard, then click and drag the lower track so that it’s just past the end of the first track, then drag it up into the upper track. Then drag it backwards and it will attach to the end of the first clip.
Then you can click [X] on the top left of the now-empty lower track to close it.
Gale
Do you have two blue wave collections one above the other? (Illustration).
If you have scrambled sound tracks, you could have stuck “Overdubbing” on by accident. That will create summary mixed tracks and it can be a little startling if you’re not expecting it.
Audacity > Edit > Preferences > Recording
what do you have selected there?
Koz
If you have overdub on and find that recording the second track recorded the first track as well as what you were recording, then are you recording from the correct input in Device Toolbar ?
You would get the first track bleeding into the recording of the second if you were recording from stereo mix (which records computer playback) or if you were were recording from a microphone but not wearing headphones.
What are you recording?
Gale