what is anti-aliasing and what does it do?

Answer 1

Anti-aliasing takes away the sharp jagged lines in graphics and smoothes them.

Think of the graphics on old computers where the pixels appeared big and sprites/graphics appeared blocky. That's what non-anti-aliased images look like close up. Anti-aliasing "fills" in the gaps between the blocky bits on the edges of lines and make them appear smoother.

Answer 2

The human eye doesn't see things perfectly - the world's a bit fuzzy! Anti-aliasing makes things look more natural by blending the colours at the edges of objects very slightly.