I have a 4-thread serger (overlock). It does 2 things....serges and will do a rolled hem - some models will also do a third stitch (similar to topstitching - can't remember what it is called).

There is no way I can explain how the loopers work!

Mine is easy to change needles (same way as changing needles on my sewing machine)

There is only one way to thread it (and believe me, it won't work properly if it isn't threaded exactly right)

You can do all sorts of 'decorative' work, i.e., make your own trim, etc. but not 'embroidery' type stitches.

I have a book called Serger Secrets which shows how to do beading, braid, cording, couching, fagoting, lace, piping, shirring, tucks, etc.

Some folks say they can install a zipper with their serger.

Folks with other brands may have other opinions.

Carolyn

Mine has five thread capability. It will do a safety stitch which is like a chain stitch as well as a four-thread overlock stitch at the same time. It will also do both a two-thread and three-thread cover stitch which looks like two or three rows of top stitching. You will see that type of application on t-shirt hems and other ready-to-wear. You also can do couching, apply beads, etc. as Carolyn stated. I also have "Serger Secrets" and "Creative Serging" but have not ventured into some of the cool stuff they show in those books. Today I made jeans belt carriers (that look just like ready-to-wear) using a serger attachment meant to do bias binding.

My newest serger is a Viking 936 with an LED screen, and I love it. I also have an older four-thread White serger.

Mary

I've linked a thread from mid-July below.

I have worked with industrial machinery for many years now and I operated the multi-needles for several years in a manufacturing venue.

To many, it may seem I'm "splitting hairs" in the last reply to the linked thread, but the subtle differences are important when selecting the appropriate machinery for specific applications.

Until you have a basic picture of the subtle differences between the configurations available you won't be able to really understand the interplay between the needle(s) and the loopers and/or spreaders.

Here is a link that might be useful: A Recent Thread on Overlock machinery