Learning to distinguish between shapes is essentially an early form of reading. Children who can tell which shapes are which, can better differentiate between different letters when they progress on to reading. Being able to recreate shapes also helps with writing. Most letters are based on a combination of circles and squares, or lines at right-angles to each other. Some letters, like X, R and Y use diagonals, the building blocks of triangles. This applies to learning numbers, too.
Shapes also provide early experience in sorting and classifying. Shapes have unambiguous characteristics and so cannot easily be confused with one another. If you want to teach a child to sort, you don’t give them a pile of subtly different objects, like leaves or buttons, you use shapes (and colours).
Many toys and games involve shape recognition – start out with puzzles and shape sorters before moving on to construction and eventually drawing your own shapes.