Text Properties Dialog "Font" Page
This page lets you change the fonts used for displaying the text in your text object. Bring this page up by clicking on the "Font" line in the listbox on the left side of the text properties dialog.
If you had a section of text selected when you launched the text properties dialog, changes on this page will only affect the text you've got selected. If there's no text selected, your font changes will apply to all the text in the text object.
You've probably seen controls resembling all the ones on this page before. The "Font" dropdown list lets you choose a different typeface. The "Size" dropdown list lets you choose your font size. The Bold, Italic, Underline, and Strikeout checkboxes let you apply (or not) these effects.