Open a document in your word processor.
The upperish menu bar has a small windiow that has font name (Ariel, New times Rroman, etc) with an arrow beside it that when clicked shows the available fonts. (There are more fonts available on the web)
Next to that is a window with a number in it , probably a 12 or 14, with a down arrow next to it. Click on the arrow and a selection of font sizes appears. Select a different number and what ever you type from that popint on will be that font size and style, the bigger the number the bigger the letter.
Write a document, highlight a section of text with left mouse button, move to the font selector (size or style) and click, highlighted text will change to what you've selected.
Move the cursor anywhere in a document and click. The font style and size for that location will show up in the windows.
To the right of the font selectors are selection for italic, bold and underlined. These work the same way as the font selection. Same as on this forum
Font size is really neat for school kids who have an assignment of "one type written" page. Bigger fonts take up more space on the paper. Of course you could stupid with that but one or two points is very hard to "see" a difference in.