Question

how can a compound be both polar and nonpolar

Answer 1

A compound's chemical structure can be such that part of it is polar and another distinct part non-polar. For example, an alcohol? But that would be considered polar-covalent molecule.

It's possible to have a non-polar molecule with polar bonds, which would be the best answer to this, I think. If bond dipoles cancel, the molecule is non-polar.

CO2 or carbon dioxide is a non-polar mol'c w/ polar bonds.

Answer 2

It's a linear mol'c, which is why the dipoles cancel. Not always the case, ofc
The C=O bond is polar, but the molecule as a whole is non-polar.