If you need to check the fare rules for a train ticket after booking, you can access the itinerary at any time via the My Trips tab or the Upcoming Trips section on your landing page.
Simply click on the relevant trip to view the full itinerary. Then, select the specific trip component (such as the train segment) to see all related details, including fare conditions.
Under the journey details you will see a link giving you full details regarding your booked fare.
For more information on UK trains, have a look at the Rail User Guide.