mixing tracks

Audacity 2.1.1
Windows 7

I have been mixing tracks for a long time, so I don’t know why I can’t seem to do it now.

I have one set of stereo tracks with recorded material. I open another blank set and paste the recording to mix, but instead of appearing under the 1st one, it pushes the 1st one ahead. What is wrong?

Try adding a new track, and paste into that.