Plucking occurs when rocks and stones become frozen to the base or sides of the glacier and are plucked from the ground or rock face as the glacier moves. This leaves behind a jagged landscape.
Abrasion occurs when rocks and stones become embedded in the base and sides of the glacier. These are then rubbed against the bedrock (at the bottom of the glacier) and rock faces (at the sides of the glacier) as the glacier moves.
This causes the wearing away of the landscape as the glacier behaves like sandpaper. It leaves behind smooth polished surfaces which may have scratches in them called striations. Striations are carved out by angular debris embedded in the base of the glacier.