|Presser bar adjuster is here on most machines|
Sewing ordinary stuff, the fabric will pucker if the presser is too hard or, if it's too soft, uneven stitches will result.
Testing and adjusting is really easy and will take you less than a minute (more like 15 seconds) to check. You might even test it every time you change fabrics (I do).
1. Put fabric under the foot, leaving the needle up
2. pull the fabric back gently.
3a If it slides back pressure is too low so screw it in a little and test again.
3b If it is very tight, lower the pressure (there's usually a screw adjuster at the top of the presser bar) a little at a time until it starts to move. Now it's just slightly too loose, so turn it in about 1/4 of a turn.
4 Perform a test sew.
Your stitches should be perfect and never pucker, even if you're sewing silk (use a microtex needle for silk).
Next will be how to set the thread tension