When you start playing Pokémon Sword & Shield, you'll need to decide who your starter Pokémon will be. You can choose between Grookey, Sobble and Scorbunny. Thankfully, you can also get the ones you don't choose by taking advantage of a couple of the game's features.
Your currency for getting the other two starters will be your starter, as the idea is to trade with people who are looking for whatever Pokémon you choose in exchange for theirs. Because you can't just swap your appetizer if you want to have all three, you'll have to get your hands on an Ditto.
Ditto can breed with your starter Pokémon, producing Pokémon Eggs that will give another Pokémon the same species as your starter. After that, it's simply a matter of finding a player who is looking for the Pokémon you have and is also raising their stock appetizers for trade.
To breed Ditto and your starter, go to the nursery on Route 5. Leave your Ditto and starter Pokémon with them for half an hour, then return. If it spawned an egg, add the egg to your party and then play the game. You have to build travel distances for the eggs to hatch, so an easy way to do this is to use the fastest method in the game.
And that's all, all that's left is to try and find a player who is looking to trade. I would suggest starting in the comments section of the video linked above. We hope it will become a nice center for people looking to exchange beginners with each other.