What it is
Paste is a bait and a method. You mix fishery micros or a dedicated paste powder to a consistency that stays on the hook through the cast (or the ship-out) and comes off in the fish's mouth. Soft enough to suck, firm enough to stay on.
It is at its best on the pole, on the deck, over a small bed of micros or nothing at all. F1s love it. Carp in the edge love it. A waggler or a feeder can present it, but a pole puts it on a sixpence without it flying off.
Too sloppy and it leaves the hook in mid-air. Too stiff and they cannot suck it — you miss, or you foul-hook.