Sculling means two short oars, one per hand, symmetric. Sweep rowing means one long oar in both hands and a fixed side of the boat — asymmetric.
The fundamental split in rowing, and it shapes almost everything downstream. Sculls measure 280 to 290 centimetres and you handle two of them; a sweep oar is far longer at around 378 centimetres and is moved with both hands. The boats differ too: the spread between the pins is 156 to 160 centimetres for sculling, only 80 to 90 for sweep. A widespread misconception is that sweep rowing is the harder version. The combined blade area of two sculls is larger than a single sweep blade, so scullers actually handle more water pressure. Sweep is not tougher, it is more asymmetric: your torso rotates towards the oar on every stroke, and your side is assigned, not chosen by feel. Both share the legs-body-arms sequence; what differs is the grip, the balance and how the load splits between left and right.