What's the difference between astigmatism and myopia (nearsightedness)??

agreed with DCG.

nearsightedness assumes either a "too curved" cornea (refractive myopia) or a "too long" eye (axial myopia), or both. that means: see okay up close, but bad far away.

astigmatism assumes that some portion of your refractive system is not spherical. usually this equates to a CYLINDRICAL shaped cornea like a soda can instead of a spherical shaped cornea like a basketball. people with astigmatism-only usually have the same not-so-good vision at distance that they do at near. both blurry far away and blurry up close by approx the same amount.

it is possible and common to be both nearsighted and have astigmatism. that would be having a "too long" eye AND a cylindrical cornea, or having a "too curved" eye AND a cylindrical cornea.

Nearsighted is when you can't see distances. Astigmatism is when there is a unique curvature of the eye, making correction, especially with contact lenses, tricky and sometimes impossible.

myopia is a nearsightedness (so you have troubles seeing things that are far away), and astigmatism is is basically how the shape of your cornea is. if you have astig., your cornea is shaped like a football as opposed to sphearically. when you have glasses made, to correct myopia, the lens is concave in shape. if there is astig. needed for your correction, is set at a specific degree (basically how the lens is turned), thus refracting light into your retina as if your cornea was sphearically shaped.