Bias binding is a binding made from strips of fabric that have been cut at a 45 degree angle from the selvedge edge.
First, the true bias must be determined.
You can line up an acrylic ruler so that the 45 degree angled line is along the selvedge edge. Make a cut along the edge of the ruler.
Another way, is to fold the fabric corner up at a 45 degree angle so that the raw edges are aligned . Press the fold.
Open the fabric back up and cut along the folded line.
Make subsequent cuts along that 45 degree line
Next, sew the strips end to end until all are joined.
This method works, but is a bit of a pain. It also involves a lot more math to determine how much binding you will get from a piece of fabric.
Using the "Continuous Bias Strip Form A Square" method is easier and more accurate for determining how much fabric to start with.