Cut them into thin slices and put into a large bowl.
In a separate small bowl, mix the sour cream, dill, vinegar, salt, sugar, and garlic together until combined.
Pour over the cucumber slices and mix until all coated.
Put in the fridge 1 hour before serving. Serve cold.
Notes
For the best flavor, allow the salad to chill in the refrigerator for at least 1 hour before serving. This allows the flavors to meld together and the cucumbers to stay crisp.