Lay your rotary mat out so that the 18-inch edge is parallel to the bottom edge of the table and there is table space to the right of the mat. Lay the fabric out on the mat with the folded edge parallel to the bottom edge of the mat, leaving 1/2 inch of mat showing at the bottom. The bulk of your fabric should be to the right and smooth and flat. Align the 12 1/2-inch square rotary ruler with the fold and a small distance in from the left edge of the fabric. Lay the 6-inch by 24-inch ruler next to the square and to the left; they should touch along the length. Firmly hold the long ruler in place with your left hand and remove the square with your right. Pick up the cutter in your right hand and pull back the safety guard. Place the cutter at the bottom edge along the ruler edge. Your left hand should be firmly holding the ruler in place and it should be at least 1 inch from the cutting edge. Roll the cutter part way up the edge of the ruler and stop; do not lift the cutter. While easing the pressure on the cutter, lift your left hand and move it higher up the length of the ruler. Firmly holding the ruler in place, complete your cut along the length of the ruler. This results in a squared edge from which to begin cutting for your project.
To cut strips, start from your prepared edge. Lay your ruler along the edge with the ruler overlapping the fabric the required amount. Be sure the ruler extends the full width of the fabric with a bit of ruler showing above and below the fabric. Hold the ruler firmly and make your cut. Take care to move your left hand up the ruler as you cut and to not jostle the ruler while cutting. These strips can then be used as is or cut again to make squares and rectangles.
To cut squares from a strip, lay the strip lengthwise down the long length of your cutting mat. Have the bulk of the fabric to your right. Trim the seam allowance as was done to square up the original edge of the fabric. Cut the required number of squares from the strip using the 6-inch square ruler, being sure to maintain your cuts at the same width as the strip.
Cutting half-square triangles is accomplished by using the angle lines on your ruler. Lay a square on your mat. Align the 45-degree angle mark on the ruler with the left edge of the square so the edge of the ruler runs diagonally from corner to corner. Make your cut, holding the ruler firmly.