If you have the WavePad program, I would suggest using that to accomplish this task. But the procedure would be pretty similar with either program. As far as terminology, you can look at a track as a complete unit, often made up of different clips.
When you loaded the tracks into MixPad it stacked them vertically as separate tracks, which will play simultaneously across the horizontal timeline. This is the basic usage of a mixing program – to combine elements into one mix.
It sounds like what you want to do (create one continuous track) is have one track follow another, something better suited to WavePad, but I think you can accomplish it with MixPad. Select the track that you want to follow the first track, copy [ctrl V on a pc], position the curser at the very end of the first track, and paste. Note that MixPad will identify the pasted segment as a ‘clip.’ With track one selected, choose ‘Merge Clips’ from the Edit menu.
Do this for each ‘track’ in the order you desire. You can probably also just paste each clip onto the first track and then merge them all at once…(Once a clip has been added and merged to the first track, I would delete the original from the project.)
Once you are satisfied with the complete new track (and done any other editing you might wish like fades, add silence, or whatever) I would first ‘Save’ the project (and it is recommended to choose a folder location of your own so you can easily find it again) and then ‘Export Project As Audio File’ – under File Menu – again to a location of your choosing.
Hope that helps and makes sense.