Open an existing or record a new file.
Tap on Import / Mix and in the menu on “Mixes the current file with another file”.
Choose a file and tap on Open.
In the dialog “Mix files” you can set the audio level of the current file and the imported file.
If the checkbox “Increase the selection if imported mix file is longer” is checked, the result duration will increase at the end, if the imported file is longer than the end if the current file.
Set the desired start position with the start selector . It is the startpoint to mix in the second file.
Click on Play for preview to verify the startposition and the mix volumes of the two files.
Tap on “Apply” to mix the two files. You can see the mixed result between the start and end selector.