I was wondering, do you have to use a stabilizer for all kinds of fabric,

If depends how many stitches the design has. You can get away without stabiliser on denim and heavy calico if the design is simple but don't risk it if it is more complex!

Pam, it depends on what you are going to do with them - a light embroidery design - might work well without a stabilizer - but anything that is thread intense will always need stabilizing - so that the threads have something to hold onto - the material can ripple or pull in from the thread count.