There is no one single form or discipline that can be considered a movement to practice. By its very nature, a movement practice is open-ended, it is a research into body and mind in movement, an exploration into movement itself: into change and constant flux.
It can however be useful to start somewhere specific. The specifics you choose are unimportant. You may choose to start with a discipline that interests you the most, or perhaps you start by working on a specific body part that you feel needs an extra attention, or perhaps you look to start with the thing that scares you the most, the thing you feel is the most challenging and unknown to you.
There is no right or wrong here, any of these options is fine!
What may be most useful and relevant however, is the way in which you approach that discipline. We approach it knowing that the discipline itself, the forms we are practising, the movements we repeat - none of these are the movement practice itself. Here I differentiate between movements and movement. Movements other things we do. Movement is the constant state of change in the body, in our practice, in our lives and in the world.
An image proposed by Ido Portal is that the practice (and here I am paraphrasing) is a container: it is the cup that holds the water. Movement is the water. The water could also be held in a bowl or a glass or a jug, but it would still be the water that we are interested in. Sometimes we get confused and we start chewing on the cup instead of drinking the water (again, I am paraphrasing his metaphor here).
I think what he is trying to say here, it’s simply that the thing with practice is not the thing itself. My movement practice is not handstands, climbing or flow acrobatics. Neither is it the sum of all the individual forms I practice. Movement is the concept behind all those things, and we approach each of these to uncover movement itself. In other words to uncover ourselves.
To study movement is to study ourselves in movement. To notice how we feel as we move. Noticing physical sensations (both pleasant and unpleasant): warmth and coolness, aches and pains, softness and strength, tiredness and energy energy; noticing emotions (both pleasant and unpleasant): fear, anxiety, frustration, joy, excitement, calm…
To study movement is also to develop an understanding (not an intellectual understanding, but an embodied understanding) of how we move, of how our own body moves. It means understanding our limitations and the strengths, our own creativity, and how to apply our body to whatever task is at hand.
To study movement is also more than both these things, but what it is that is more than this I cannot fully explain. Words are not always enough to articulate the embodied experience.