Place on top like a cover. Wet it down to help with moisture.

I like to use a peice of old carpet the same way

I use the burlap in both my bins , in the factory 360 wet it once and forget it it stays moist in there, but in plastic homemade job its hard to keep it moist. I have to keep the lid cracked so it doesnt get too wet in that one or the worms will try to come out. Still its hard to keep that burlap moist.