At the right side of the main window are buttons labeled like so:
These are special commands called Popups because a new window 'pops up' from which you can choose a letter/digit/word.
É is for characters with diacritical marks. Mostly used in French but also in English with words like naïve and résumé.
Lang is present when you have multiple active languages.
Suf is used in English for a variety of suffixes.
$!% is for punctuation characters. All special characters appear here.
1-9 is where digits and arithmetic operators are chosen. You can choose many in a row keeping the popup up. Choose Done when you are finished.
Cmd is for accessing a variety of other commands such as Quit, MailMe, Call, Color, Abbr, AddW, TopW, Define, Synonym, Remote, Bounce, Match, Sudoku, and UnScram.
In all of these popups there is a way to cancel it by choosing a blank area (or Done).