Peel the carrots and daikon radish. You'll need about 2 carrots, and 1/3 of a medium daikon radish. First cut them into planks, and then into matchsticks. You should have about 2 cups of each.
Toss them with the 1 tsp of salt and sugar and let them rest for 20 minutes to draw out the moisture. You can rinse them after word and then pat them dry with a clean towel or paper towel. Add them to a large mason jar or similar.
Whisk together the 1/4 cup of sugar, water and vinegar until the sugar is dissolved. Pour over the carrots and daikon and ensure they are covered. Add more water / vinegar if needed to cover. You can use them right away, and can keep the in the fridge for up to one month.