Line a 20cm (about 5cm/2 inches deep) cake tin with baking parchment. A good tip to line the cake tin is to fold a piece of parchment into four into a rough square. Fold the square diagonally, so that the two folded sides line up and you have a rough triangle shape. Fold once more in half, bring one folded side to another so that you have a thin triangle with a point. Then line the point of the triangle up with the centre of the tin and cut the triangle along the outer curve of the tin. Unfold and you are left with a circle of parchment to fit your tin perfectly.
This page is helpful if you need to visualise this part better!