Auto tabs filling

Are you talking about guitar (and similar) tablature?

If so, create the guitar staff normally, either during new file creation or from the Instrument tab. Don't create the tablature staff at this time, only the "dots" staff.
* From the score, go to the Instruments tab and expand the guitar staff entry.
* Click on the entry for the staff, probably named "Treble clef 8va bassa" (if you're doing an instrument other than a guitar, it might be named differently).
* Click on the gear at the end of the entry and the screen that appears will have a button to "Create linked staff". Click there.
* This creates the SAME staff, linked. You'll now see "[LINK} Treble clef 8va bassa" below the original. Click the gear at the end of this new staff and set "Staff type" to be one of the "Tab" types. My choice is always "Tab. 6-str. full"

Now enter notes in either staff and the same note will appear in the other.

If you already have notes entered, do this and the existing notes will be added to the linked staff. However, you might have to adjust the string of a given note if you're up the neck at all.

Are you talking about guitar tablature, for example?
If so: you need to add a linked tablature staff to your guitar. Open the instrument dialog (i).
Select "Staff 1" for the guitar and press "Add linked staff". Change the staff type from "Standard" to the desired tablature type.
You can then write the notes either on the standard staff or on the tablature staff. The other will be written automatically.