Now, if you want your fabric to be perfectly square and without random seams, this is not the method for you. If, however, you simply need fabric with which to sew, this will suit.
I wouldn't try this with small pieces, whatever small means to you, unless you are looking for a way to fill up several hours. I tend to use legs from pants muslins that didn't fit or larger scraps that are left when I cut out pattern pieces.
If I was super patient and had a convenient place to spread out, I would roughly square up all my scraps before sewing them together, but since I am possessed of neither of these when sewing, I eyeball things as I go and trim off excess seam allowances later.
I line up, right sides together, two pieces. Be sure the grain line goes in the same direction. This can get frustrating when two pieces seem to make the perfect rectangle, but then can't because their grain lines are going in the opposite directions.
I think there is a gadget to help keep a straight seam in these situations, but I don't have it. Anyway, for my purposes here, close is good enough.
Also note, there is no need to backtack the ends of the seams as you will be cutting through the middle of the seam when you cut out your patterns. For now, all you need is the same size stitch that you will likely use for your project and a stitch small enough that it will hold the pieces together, even when the seam is cut through.
Once I have added all the pieces that I can, I use this like a regular piece of fabric to cut out my project. If this is a project I want to look nice, I will iron out each seam before I start cutting, but I mostly use this kind of fabric for experiments, so I don't worry about ironing most of the time. Also, because I don't at least partly square up my edges before I stitch the pieces together, I have some slightly curved seams that create bubbling. I fold this excess fabric over however I need to in order to make the fabric lie flat for cutting. Sure, this means I have a weird pucker of fabric in my project, but I don't care for experiments and for actual projects, I use this as a design feature.