Brahmari is a female bumble bee or humming bee.

Technique:
Sit in any meditaitve asana.
Fold the tongue and touch the upper palate with the tip of the tongue.
Take a deep inhalation.
As you exhale, make the humming sound.
This is one round.
Repeat it for 5-10 rounds.

Benefits:
It calms down the mind.
Good for insomnia.