Many, if not most, of the sources we all use are protected by some kind of copyright. Facts can't be copyrighted, though, just their presentation, so any facts you find can be used. The text portion of a profile should generally be in your own words, although you can quote small portions of books as long as they are properly cited. If the book is a compilation from other sources, it's always best to try to find the primary/original source for the information. Good source books are documented.
All facts should be accompanied by a proper source citation which gives the author, title, publisher, location and date of publication and the page in the book. There are a variety of formats for presenting that information. The purpose of the citation is both to give credit to the person who created the work and also to enable others to locate and verify the information for themselves.
The "Sources" help page - Category: Sources Help (wikitree.com) has lots of great information and links to the style guide.