To determine whether you need to seek permission to use the work of another, ask yourself these three questions:
If you answer yes, or maybe, then continue.
Remember that facts and ideas are not copyrightable, but the specific expression of them may well be.
Also remember the obvious: photocopying, scanning, faxing, etc., always involve using the expression of another.
If you answer yes, or maybe, then continue.
Remember that works in the public domain are not protected by copyright, but that organized summaries or compilations of such work may be.
Remember that certain works cannot be copyrighted, such as works by U.S. Government employees, some simple (even if lengthy) listings, certain blank forms, etc.
If you answer no, or maybe, then seek permission, as described.
Some, but not all, educational uses fall under the principle of "fair use," which will be discussed next.