kumbha = pot (a traditional image of the human torso as a container for the breath with two "openings" at the throat and base of the pelvis)
antara (ahn-TAH-rah) = interior
bahya (BAH-yah) = outer
Step by Step
Antara Kumbhaka requires the application of both Jalandhara and Mula Bandhas; in addition the rib case gently "hugs" the lungs.
Establish Sama Vritti Ujjayi (and for this example, the vritti count is 6 OMs). To begin, apply the two bandhas as you near the end of your inhale, and retain the breath for 2 OMs, no more. Gently squeeze the ribs against the expanded lungs. Then exhale, concurrently releasing Mula Bandha and, when finished, raise your head to neutral. DON'T perform Kumbhaka on successive breaths; take 2 to 3 Ujjayi breaths before the next retention.
In general your first Kumbhakas should be one-third to one-half the length of your Sama Vritti count. Practice at this level until you're completely comfortable, which may take several weeks or longer.
Then gradually reduce the number of Ujjayis between Kumbhakas until you can comfortably retain your breath for 2 OMs on successive inhales for about 5 minutes. Next increase your Kumbhaka to 3 OMs, but again separate them by 2 to 3 Ujjayis. Again gradually reduce the Ujjayis until you can comfortably retain for 3 OMs on successive inhales for 5 minutes.
Proceed methodically until your Kumbhaka count matches your Sama Vritti count. Now STOP. Don't go any further without direct guidance from an experienced teacher.