Genealogy involves gathering information about various family members from a wide variety of sources. To be meaningful, you will want to share your findings with others. When you do that, you are making the information public, that is, publishing it in some form, be it a book, a web site or simply transmitting a gedcom file to another researcher.
The right to publish or copy your own original work is the basis of copyright law that provides you with some form of protection against others using or reproducing your work without your express permission.
The flip side of this is that during the course of your research, you will no doubt build on the work of others by using an index, an article, a published list, another genealogy etc. Respect the rights of other researchers and give credit where credit is due. If you intend to use anything beyond the shortest of quotations, it would be prudent to obtain permission from the author or you may be guilty of copyright infringement.
Much space can be contributed to definitions of copyright and interpretations of what is or is not infringement. For detailed information, refer to: The Canadian Intellectual Property Office, Industry Canada
In general, you may make a copy of something for your own personnel use or private study unless the author specifically prohibits such copying. Also, in general, you may incorporate a piece of data or information you found into your own family file and cite the source of the information. By information, we mean something very specific, like a birth date. If you are intending to copy anything more than this, you should seek permission from the copyright holder before reproducing or passing it along to others.
Various institutions have developed policies or guidelines about copyright issues.
Archives of Ontario: Customer Services Guide 108 discusses their policy, what copyright means to your research, and how to request permission to publish information that you have obtained from the archives. For more information, see:
Copyright and Your Research: Archives of Ontario Customer Service Guide 108
Library and Archives Canada: Before reproducing material from the website, please read important copyright information at: Important Notices: Copyright