A trade deal defines the things which can/cannot be exported to a country, the quantities, and the standards to which they must conform (materials and ingredients, safety features, packaging and so on) If we wish to sell to EU countries, we will need to conform to those standards.
The same applies to any other country with which we trade. For years we have beeen able to put "CE" onto things to show that they are up to the standard required by EU regulations. Importers round the world knew what they were getting. Will we still be able to do that when we are no longer a part of the EU? If not, what quality mark will replace it to maintain confidence in "Made in Britain"? THe kitemark?