Font Gallery - Apply Button
The Apply button in the Font Gallery applies the selected font to the currently selected text objects and regions.
A font can also be applied by dragging a font over a text object and dropping. Dropping onto a selected region applies the font to that region otherwise the font is applied to the whole text story.
If you want to apply a font to a single character either:
select the character then drag-and-drop the font onto the character (see Selecting text),
or start dragging the font then hold down CTRL. You can then drop the font onto the character without having to select it first.
If the selected font is currently not installed, it is installed when you apply it.
You can also apply fonts by double clicking them in the gallery, this will apply the font to the selection. CTRL-double-clicking will apply the font and close the gallery.