They’re hollow tubes sometimes known as snakeskins of sylnylon. nylon or mesh that slide over the tarp, the cordage for hanging them is tucked in each end so you can hang the tarp snake up without deploying it. The sleeves are either 2piece/halves that can be slid off each end to deploy the tarp, or 1 piece full length. DDhammocks sell them https://www.ddhammocks.com/product/dd_x ... from_cat=2
As my tarp is 13ft and slightly longer that regular 10ft-12ft tarps, stock snakeskins are slightly too short for it, so I got mine from Warbonnet to match the tarp
A couple of videos of them in use