Rethinking, reorganizing, and rewriting some area of interest makes the creator think the subject matter through thoroughly and thus gives him or her an opportunity to make a real addition to the scholarship in that area. Of course, if nothing is copied, the writer of the document can not have a copyright problem because the copyright law only provides protection against unauthorized copying of protected works. But if you have to copy something, make sure it is in the public domain or is covered explicitly with a proper consent.
Safety lies in writing one's own materials and giving proper credit for the sources that are used.
Read the 10 Big Myths about copyright explained , especially the Summary at the end. Remember that copyright law protects the expression of an idea, and not the idea itself. Thus, you don't need to worry about violating a copyright if you don't copy the work of another. Remember also that materials are copyrighted when written, so an absence of a copyright notice does not mean that the writing is in the public domain. Writing your own materials in your own words to communicate well with your intended audience will increase the educational value of your Entry and will teach you writing skills.