If you start doing a lot of sewing, sooner or later you're going to need to change the needle and/or presser foot.  Needles become duller after a lot of use or sometimes they simply break.  Sometimes you're just working with a different kind of fabric.  Not all machine needles are the same.  This video shows you the difference and how to easily change a needle.  Included in this video is how to change the presser foot so you can use the different foot attachments for your machine for variety of uses such as for a zipper or for doing a buttonhole.