To clarify, what you really need is a foot note and not a footer, also what version of Microsoft Office are you using?

Assuming your using Microsoft Word 2010, here is how you insert a footnote:

Insert a footnote or an endnote
Microsoft Office Word automatically numbers footnotes and endnotes for you, after you specify a numbering scheme. You can use a single numbering scheme throughout a document, or you can use different numbering schemes within each section (section: A portion of a document in which you set certain page formatting options. You create a new section when you want to change such properties as line numbering, number of columns, or headers and footers.) in a document.
When you add, delete, or move notes that are automatically numbered, Word renumbers the footnote and endnote reference marks.
Note If the footnotes in your document are numbered incorrectly, your document may contain tracked changes. Accept the tracked changes so that Word will correctly number the footnotes and endnotes.
In Print Layout view (Print Layout view: A view of a document or other object as it will appear when you print it. For example, items such as headers, footnotes, columns, and text boxes appear in their actual positions.), click where you want to insert the note reference mark.
On the References tab, in the Footnotes group, click Insert Footnote or Insert Endnote.

Keyboard shortcut To insert a subsequent footnote, press CTRL+ALT+F. To insert a subsequent endnote, press CTRL+ALT+D.
By default, Word places footnotes at the end of each page and endnotes at the end of the document.
To make changes to the format of footnotes or endnotes, click the Footnotes Dialog Box Launcher, and do one of the following:
In the Number format box, click the format that you want.
To use a custom mark instead of a traditional number format, click Symbol next to Custom mark, and then choose a mark from the available symbols.
Click Insert.
Note This will not change the existing symbols. It will only add new ones.
Word inserts the note number and places the insertion point next to the note number.
Type the note text.
Double-click the footnote or endnote number to return to the reference mark in the document.