About
This article will explain how to set your vacation responder. This includes setting a permanent one as well.
Environment
The linked article shows how to do this on both desktop and mobile environments.
Steps
View Google's article explaining how to setup a vacation responder in Gmail. Note that the link provides options at the top to view steps based on Computer, Android, or iPhone & iPad.
Hint: (If you would like a permanent responder, leave "Last Day" unchecked.)