Here's a cool trick... cake recipes will often call for lining a round cake pan or round springform pan with parchment paper. Parchment paper (or waxed paper) doesn't come in nice circular pieces. So here's how you create one with just a few clever folds and a pair of scissors.
Start with a square piece of parchment paper.
If you don't have a square, fold your rectangle into a triangle like the picture below by folding the bottom left corner up to the top edge.
Cut off the extra edge, unfold... and you have a perfect square.
Fold the square in half - bottom edge up to the top edge so the seam is on the bottom and the opening on the top.
Fold in half again. This time taking the left edge onto the right edge.
Next fold into a triangle by bringing the top left corner down to be on top of the bottom right corner.
Fold into a smaller triangle by bringing the diagonal edge down to be on top of the bottom edge.
Hold the folded paper over your pan so that the point is in the middle of the pan.
Cut the triangle along the curve of the pan side.
Open the cut, folded paper and you have a perfect circle! Ta-Da!
Place the circle of parchment paper in the pan. Grease if directed by your recipe. Fill with your batter.