Just in case I'm not here when you answer, I'll just explain where to find friend codes and how to add friends now.
Finding your code: Go to the home screen and select the user image in the top left corner of the screen. Once you select 'profile', you'll be able to see your friend code right next to your picture, it should start with 'SW' and the rest should be three sets of four numbers. Note that you need a Nintendo account to have a code and to register friends, so if you do not see your friend code, you will probably have to create an account.
Adding friends: Again on the home screen select the user image in the top left corner of the screen and then select add friend. There are a couple of ways to add a friend, but select 'Search with Friend Code' to add a specific person. You can test it out on me if you want, my friend code is SW-0894-2314-1709. If you want, you can also try other methods that might be able to find friends with the options 'Search for Users You Played With' and 'Search for Local Users'.
PS: Make sure you have a Nintendo Switch Online subscription, as it is reauired to trade Pokemon online.