I typed in my text, was able to slant, make bolder, underline, color and select which font style I wanted and so on but I can’t find where I can change the font size.
Do I have to buy a plug in for that???
If I selected all the text on that page I could use the plus and minus keys on my iMac to increase or decrease the font size but after saving and publishing the site it had not changed to the smaller size???
On styled text you select the text that you want to make larger and hit the ⌘ Cmd+ for larger and ⌘ Cmd- for smaller text.
That should add wrap the text with a html span like this: <span style="font-size:25px;">
That will in most cases change the font size. However, depending on the theme you are using, it might get overridden.
A URL to the published page will help us figure out what has happened.