When you are entering or modifying a listing in Matrix, there are three buttons at the bottom of the screen, regardless of which tab you are on:
The Validate button's sole purpose is to check all of the required fields on the input form and alert you to any that you have missed or filled out incorrectly. When entering a new listing, validation only happens if you have the status tab set to Active or Coming Soon. If you have the status set to Incomplete, clicking Validate will not do anything.
*** Clicking Validate will not save your work! It is simply a quick way to see if you have missed any required fields. The only way to save your work is to click the Submit Listing button. ***
You do not need to use the Validate button. You can save your work without ever using it. When you go to save a new listing, Matrix will automatically check all required fields when you click Submit Listing, and will flag any tabs where there are problems.