The process is a simple one. Stitch strips of fabric together and then cut the resulting panel to lengths, such as for blocks in a Rail Fence quilt.
Image from “Sew a Simple Rail Fence Quilt Block With Pre-Cuts.”
However, there are places that this simple process can go wrong. For example, inexact seam allowances can produce blocks that are slightly off in size (which will multiply over the span of a quilt). It’s also easy to produce curved strip sets rather than straight ones.
Kathy Patterson demonstrates the process of creating accurate strip sets in the following video. It’s an excellent one that will show you how to avoid many of the potential pitfalls.
If you’d like to see how strip sets become blocks, watch the following video. It demonstrates the creation of strip sets and cutting them apart for 9-patch blocks.