Fill a plant pot half way with organic, peat-based potting soil. Water the oregano the day before you want to transplant it so the soil is easier to handle.
Use a hand spade to dig the oregano out of the garden. Dig in a circle around the plant and then underneath the oregano, getting up as much of the roots as possible. Loosen the roots with your hands.
Lower the oregano into the plant pot. Fill it the rest of the way with the potting soil until the oregano is at the same depth it was in the garden. Water until the soil settles.
Place the oregano pot inside, in a sunny window that gets direct sunlight.