Your application will automatically save each time you respond to a question. There is no need to click any buttons to save the application. As you respond, you will see a green "Saved" with a checkmark next to each response.
You can safely exit your application and know that every response you fill out will be automatically saved in the system. In the top right-hand corner, you can see the date of the last auto-save activity. Feel free to check that date before you exit your application to know that all the information has been automatically saved.