Many a times while reading books you might have seen a star or number just on top of a word or an image and you look around at the end of the page there is a small not for that. This is called as Footnotes and Endnotes which in dictionary means “A note of text placed at the bottom of a page in a book or document. The note can give an author’s comments on the main text or citations of a reference work in support of the text, or both.”
Microsoft Office Word 2010 has this feature available and can help you author a book or document. You will have to use the References tab and then look for Insert Footnote option there. ( Alt + Ctrl + D is the shortcut )
Just use the shortcut where you want to add the note and you will see it appearing at the end of the page for you under a line.
Like you can see in the image above, this option can be completely customized from the default in roman. If you would like to make use of certain symbol, reset it on every page and opt for either at the end of document or end of page. In my opinion it should be at the end of the page unless you have very handful of such notes.
Also if you click on Next Foot Note, which is a drop down, it allows you to navigate between footnotes / endnotes quickly. Show notes is used to quickly move from symbol used to footnote where you have written all the details.