Similar to applying plaster, this texture is achieved by applying drywall mud using a drywall trowel, and then skimming the mudded area again with the cleaned trowel to smooth it out. Hand troweling ...

Drywall nails will also do the job ... creating a trough. Taping trowels have a little bend in them, so when you press them ...

After the texture dries on the wall for about 15 minutes, use a drywall knife or trowel to gently press down and flatten the texture. Use a light touch to avoid flattening the texture completely.