Question

GEOMETRY... when you name a plane using 3 letters does the order of the letters matter

Answer 1

No, the order does not matter.

Sometimes, depending on the question being asked there can be an order that is easier to use (for example if the plane is represented in a drawing it can sometimes be nice to name the points from left to right or top to bottom as they appear in the drawing, or you might like to name the points alphabetically) but this is NOT required and is not "more correct" than any other order.