sheer means you can see through it, usually applied to women’s clothing: She wore a sheer silk nightgown. It also means “very steep”: The sheer cliff loomed above them. And it’s occasionally used as an intensifier: The sheer effrontery of his suggestion enraged her.
As a verb, “sheer” is used like this: He sheered away from the cliff; He sheered off down a little-used road.
shears are scissors: He cut the silk with his shears.
As a verb, “shear” is used in the sense of cutting: He sheared away (or sheared off) some of the excess.
There’s “wind shear” as well, and other “shear forces”, meaning forces that push at an angle.
Your best move if you want to use one or other of these words is to check the dictionary to make sure you’ve picked the right one.