If your tear is at a seam then it’s likely an area of high stress and should probably be reinforced, glued and stitched….all three. Repair method depends on the severity and whether you plan to do it while the fabric is relaxed, or while the tent is up.
This stuff is awesome: GearAid ‘Freesole’ aquaseal glue, and/or GearAid Tape.
When I’m reinforcing a tear in a tarp I often use ‘Gear aid ‘seam seal’, apply a layer then immediately cover with a nylon patch (no adhesive back, cordura would be good on a shack). Smooth it out and flat as possible trying to get air bubbles out. After a few hours I’d stitch.
Stitches are like perforated envelopes, each pinhole weakens the fabric and creates a tear line.
If you are planning to sew the tear back in place while the tent is up I’d (1).sew with quality thread or braided line as another post recommended, then (2) Glue that seam with the Aquaseal ‘Freesole’.
(3) probably use an adhesive backed tape ie Gearaid on the whole thing after its dry.
Amazon: search gear aid aquaseal
These products are great to have around
Good luck