You can also use small blocks as your corner stones such as stars, 9p's, etc. Anything that is square & the same size as your sashing & borders.
Gotta love a quilters lingo & shorthand............cornerstones, dogears, FQ, PP, FMQ, etc. here is a site that may give meaning to some of them for you!
http://www.quiltaholics.com/glossary.htm