Hi, I'm new here and I'm so glad I found this place!

I recently bought a new serger. It's a Brother 4 thread. I'd like to be able to sew with it but when I do I can pull the seams apart pretty easily. So, I sew the seam on my sewing machine and then finish the edges with the serger. I've adjusted everything I can but still don't know what's wrong. I've never used a serger before. I would appreciate any help!
Lynn