顔 means just "Face" but 面 means like "Side" for example 顔面(face side) 背面(back side) actually, 面 has mean "Face". but it's a little bit old and sometime offensive.

人間の顔面の形や表情を表す意味の場合、 面【つら】は顔【かお】よりぞんざいな言い方です。 In context of human face shape or expression, 'tsura' has impolite, rude or careless savor.

Hi, They both can mean face, but 面 is pronounced as つら　(tsura). And it is kind of a rough / dirty way to say face.