Tarps are made from various plastics, such as vinyl and polyester, and from canvas. All tarps are subject, at least to some extent, to damage from abrasion and from UV rays, and may need to be repaired.
The two main ways of repairing a tarp are gluing and sewing. Grommet replacement is a related type of repair.
All sorts of plastic and canvas tarps can be glued. Follow the manufacturer's instructions for the particular patch kit being used. These patch kits typically contain a fabric patch to match the tarp and adhesive, but kits containing tape are also used. It is advisable to apply a waterproof coating to the patch after it dries.
Canvas tarps are the only kind that can be sewn. You can either sew on a patch or darn a hole or tear. Use sturdy thread made of the same material as the canvas.
You sew a tarp using a heavy-duty machine or by hand with a special needle called a sailmaker's needle.
Sewn repairs also need to be made waterproof. The traditional method is by applying beeswax, but commercial waterproofing products also exist.
Replacing a grommet requires neither gluing nor sewing. You remove the old grommet and either use the old hole or make a new one. Then you gently hammer the two parts of the new grommet around the hole.