in the menu it says "Mail for Gmail" -> so it's an application. i would try to update the application and osx. a restart may also help.
if the printing dialogue doesn't work in other applications there is something wrong with the printing software/driver and not the gmail app.
the lack of detail in your problem description makes it very difficult to help you. i think it would be best if you could find a person in real life who can help you with your problem (neighbors/relatives/friends). if you are using an apple laptop you could take it with you and ask the young people in an apple shop for help.