Copyright questions and the re-use of information found on the web  can be a difficult issue. The following information is, as  I understand it from professional counsel (see references below) and research, and not offered as professional advice (although the content of this page has been reviewed by credentialed sources for accuracy). You should refer to the US Copyright Office or the US Patent and Trademark offices for specific information.

        Intellectual property (ie writing, drawing, composing,  - any method of creative presentation) is automatically protected  under the Copyright Laws of 1976 and 1978, once the material is placed in fixed form (including but not limited to print, magnetic media, sound recording, and the Internet). It is not required to be published (that being defined as distributed to the public). Registration with the US Copyright Office is not required in order to be protected, but may be beneficial; it is very difficult to establish legal claims, if needed, without it. Copyright on material is in effect for the length of the author's life plus 70 years (in most cases - see US Copyright Law). After a copyright has expired the material is considered to be in the "public domain" and no longer under protection in terms of royalties or licenses (citation still applies).

        When you purchase or otherwise obtain copyrighted material (such as a book or recording) you may use it for your personal enjoyment and growth. You cannot copy (be it via computer processes, electronic or handwritten), cut, save, print, or photocopy/reproduce it, and/or reuse or market it for money, or under any circumstances claim or imply it to be your own work or creation. The concise limits are summarized as that it may not be republished, broadcast, rewritten, or redistributed by any means. Using someone else's work as your own is plagerism and a prosecutable offense under US Federal law. Information that is used verbatim must be quoted and cited. This also is directed to web content where it is so easy to "right click and it's yours". Links to specific web pages on another server should be clearly indicated that they lead to another website (just like you would direct someone to another book in the library), otherwise is can be tantamount to theft of content (note that this is different from simply linking in general to other websites). Using someone else's work without permission even if the source is cited, depending on content and law, may still be illegal. As stated by the US Copyright Office on its website,  "Acknowledging the source of the copyrighted material does not substitute for obtaining permission.".

        Reusing copyrighted material for other than personal use can involve permission, royalties or licenses. Copying and using the materials beyond personal use may (and usually does) require direct permission from the publisher or originator. When it is granted, you include on your copies and use of the materials "such and such used with permission of the author" or equivalent. Some expanded copyright statements outright prohibit any further use of the material. On the other hand, authors may include a disclaimer on their work that reuse for non-profit purposes is permitted. This happens often with matters of information for the public good, education or other some such worthy cause.

        Copyrighted information being used on a limited bases for non-profit education is generally considered "fair use" - for example, a page or a section of a page of a book may be given has a handout in a non-profit teaching situation, providing the source of the information is acknowledged. 

       Further confusing intellectual property issues is what falls under copyright protection versus patent or trademark protection. See the U.S. Copyright Office and the US Patent and Trademark Office website for further definitions of intellectual property and the clarifications of which protection applies to what type of intellectual property. It is however, important to remember that in virtually all circumstances one of these protections will usually be in force and applicable, so as the US Copyright Office goes on to advise, if you take the time and effort to request permission, one can rarely go wrong.