This feature works in conjunction with the Check Document Now action, which can be triggered by the shortcut ⌘+; and marks the misspelled word. Right-clicking on the selected text with the mouse will display corresponding suggestions for the misspelled word in the context menu. With the option "Automatically show spelling suggestions", these corresponding suggestions are offered as a menu and can be selected using the arrow keys and used by pressing the Enter key.
Alternatively, words underlined in red can be selected manually and the menu with the suggested corrections can be displayed by using the keyboard shortcut ⌥+ESC.
MarkMyWords also offers an extended text checking option using the Language-Tool.org web service. More information on this can be found on the following page: Text check with Language-Tool.org,