Nothing about the bandhas

Words are very useful as a means of communication - providing the person hearing the words has the same understanding of them as the person speaking them. If they don't then allsorts of misunderstandings occur and we can get ourselves into big trouble. Most of us don't realise this - that the word is not the thing - and, because of our misguided belief in the supremacy of the word, believe our interpretations of what we have heard or read. Even when our understanding of the words is correct they are always inadequate to describe a thing. There is always something more - "to see infinity in a grain of sand". So negation, saying what something is not, is actually more useful than trying to describe something because it allows us to get closer to the truth.
Take for instance the bandhas. Jalandhara (throat), uddiyana (abdomen) and mula (root) bandhas (locks) are often taught as deliberate contraction of different parts of the body. I can't tell you what the bandhas are or how to do them. But I can tell you that pulling in the tummy and 'sucking' it up isn't uddiyana bandha; squeezing the pelvic floor muscles isn't mula bandha and ramming the throat to the chest and scrunching up the shoulders in not jalandhara bandha. The bandhas are not about deliberate contraction or tension. They are locks and just as there is no force or tension involved turning the lock on a door there is no effort in 'activating' the bandhas. Effort is needed when trying to force through a lock but even then the lock doesn't expend any effort in resisting. Neither can I tell you how these ideas originally arose, maybe this was how students recreated what they saw in their teacher and it got propagated or perhaps such instructions arose as as a crude attempt to give an idea of what the bandhas feel like but was taken as the thing and propogated by students whose studies took them no further (rather like stopping the study of physics aged 14 and, being ignorant of one's ignorance, passing on what one knows and it being mistaken by others for the full story).
I'm not saying that everyone mistakes these gross actions for the bandhas. Of course there are people who have got a more accurate understanding as to what the bandhas are (and I am grateful for finding one who said "no, that's not it") but remember they who know don't tell and those who tell don't know (I guess because of the inadequacy of words). Ultimately you have to understand for yourself. And keep on understanding - infinity in a grain of sand remember.
You don't 'do' the bandhas or even 'find' them. Rather the bandhas come through you. They arise spontaneously when the correct conditions are present in the body. When they do arise, you will recognise them in a eureka moment. And you will realise then why words cannot describe them. But it won't happen while you are pushing or pulling or deliberately contracting. And it won't happen if you are trying to do the bandhas. Simply create freedom in your posture and let the bandhas take care of themselves.
And that's all I have to say about the bandhas.