Use a tissue to measure out your fabric. Cut a rectangle this is a couple of inches wider than the tissue and 3 times the height of the tissues with a couple more inches allowance.
You will need two squares of fabric, one for your lining and one for the cover.
Place the fabric squares on top of each other so that the wrong side of the fabric is facing out. Sew along the edges, leaving a small gap on one side.
Pull the fabric inside out through the small gap you left so that the right side of the fabric is now facing out. Lay it down so that the cover fabric is facing up.
Fold the two sides of the fabric in so that the edges meet in the middle, pin this along the edges.
Sew along the edges, notice that you are now sewing up the gap you left earlier.
Fold inside out again and fill with tissues, yay.