Carts without mesh are just place holders. They can be used for "dripping" but that is an advanced user technique and I would suggest just putting the empty blanks aside until you can research "dripping" on this forum.
As for refiling carts check out
Mooby's Newbie Guide to Refilling Carts. He just put it up and it's a great "how to" refill the old carts you use. If you have new blanks (with poly-fill but no
juice) just drop e-
juice into them until the poly-fill is moist all the way
through. You can tell this by adding drops until it pools a little at the top then dab the excess off with a paper towel/tissue. After a few fills you'll become a pro and won't need to dab anymore.