The pressure foot tension, also known as presser foot tension, keeps pressure on the fabric so the sewing machine feed dogs can pull the fabric through. When the presser foot tension is set correctly, you get stitches that are the same length. To sew heavy fabrics you need to have the presser foot set with light pressure, while light fabrics require heavy pressure. The pressure foot tension regulator will be either a pin that pops up or a screw found on top of the sewing machine, directly above the needle and presser foot.
Look at the top of your sewing machine to find the presser foot tension regulator. It will either be a pin that is about an inch long with a diameter of about 1/4 inch and a wider 1-inch diameter metal piece around it, or a screw with a rubbery washer around it.
Press down on the wide outer ring and the inner pin will pop up. This creates a light pressure for heavy fabric. Press down on the inner pin to create heavy pressure if you are sewing light fabric.
If your machine has a screw, use the optional screwdriver to turn the screw and change the presser foot tension. Turning the screw clockwise will create heavy pressure and turning it counterclockwise will give you light pressure.
Test the pressure foot tension on the machine by sewing on a scrap of fabric that is the same thickness as the project you are beginning.