For language learners or students who need extra conceptual support, you can introudce the concept of area and perimeter with an anchor chart like this. First, define what a "shape" is. Then, teach the words "inside" and "outside". I would use hand motions to really help students understand these definitions. Finally, introduce perimeter as the OUTSIDE of a shape and the area as the INSIDE of a shape. For English learners, the simpler the anchor charts (and the more visual) the better!