tunnings

Staff text can be used for either TAB or standard notation.
For standard musical notation it's straightforward - just list the tuning of the strings in a row of text.

If you want the TAB to look like this:

You can enter (standard tuning shown here):
E
B
G
D
A
E
as text (with each string's name on a new line) and then adjust the font size to scale it to the staff.
Alternatively, you can add (and adjust) it as an image.
See:
https://musescore.org/en/handbook/3/images