This bandh relates to muladhar chakra and is termed as mulbandh. If the bandh is to be performed ideally it should be performed in Siddhasan. Otherwise it may also be performed in Padmasan.
Position of Readiness for Mulabandha
Sit cross-legged or in lotus asana, with the spine straight.
Steps
Focus attention on the pelvic floor.
Press the suture at groin region with the heel of right foot and put the heel of the left foot at the base of the reproductive organs.
Inhale, hold breath, and contract the anal area.
Pull it forcibly in towards spinal cord and feel as if you are trying to pull the wind in your belly upward.
Retain this position as long as comfortable.
Exhale, and relax.
Do more rounds with feet interchanged.
Beginning with five or ten 'rounds' of each, and increasing gradually, not to exceed 60 rounds.
Benefits of Mulabandha
Practicing of Pranayama in this Bandha (posture) you can achieve perfection.
Practice of this posture helps to follow celibacy.
This posture awakens Kundalini
The learner who practices this posture can remain young forever.
This posture stimulates appetite; removes constipation, and strengthens the semen.
This exercise is also useful for delaying ejaculation. One should practice Mula Bandha and Vajroli Mudra one after the other.
Note
The bandh should be practised under expert guidance.
Persons suffering from hernia, piles etc should consult yoga expert before attempting this bandh.
Mula Bandha is the complement to Vajroli, and should be practiced along with it.