You hear this phrase quite often in the yoga world. One-pointed focus: meaning the experience of concentrating on one thing at a time.
As a result, tada drastuh svarupe avasthanam: and then the true self - the Seer, from drsti - to gaze - the purusa - that unchanging part of the self (versus prakrti - everything else, which is at the mercy of constant change - our bodies, our possessions, our emotions, the world around us) emerges.
There's no multi-tasking in yoga. And as a sign of how little one-pointed focus the mind has: as I wrote that sentence, I was thinking of the "there's no crying in baseball" line from A League of Of Their Own, and then about Madonna and Tom Hanks, and then realized that I was no longer thinking about yoga or focus or this post. Ah, the mind's ability to slip seamlessly from its current thought into memory and imagination and misperception.
So, we focus on our breath or our movement or a chant, which gives the mind the experience, at least briefly, to feel the experience of focusing on one thing. The more agitated our mind is, the more concrete the object of focus. For a child, physical movement. For someone with a more settled mind, perhaps a breathing technique, a more subtle and less tactile focus.
But the overall goal is to try to stick with that object. As you experience what it feels like to allow the mind to concentrate, you begin to sense - very gradually and,generally, in a very subtle way - what it feels like to allow the mind to rest, to engage with its object of focus, to move toward samadhi: that sense that you are so engaged in what you're doing that you feel connected - as when you are reading a good book, and you don't hear what your parent asked you because you're so immersed in what you're reading. (Or substitute your childhood memory here.)
This is the long way around for me trying to re-discipline myself to do my pranayama practice every morning. Because it makes a huge, giant difference in how I feel going into the day. Especially compared to not doing it and then spending time checking email and blogs and Ravelry.
...And I'm trying to downsize the number of projects that I'm working on, which is also a challenge. (Yoga aids you in recognizing yourself - as though you are looking in a mirror. And it helps "clean" that foggy mirror. But it doesn't make the behavior go away on its own. To which I say, nuts (see Rex Stout and Nero Wolfe and Archie Goodwin for that one.) Recently I volunteered to teach weaving and spinning at a local history museum. I have always sworn that I would not learn to spin, don't need one more craft to distract me. But they're going to teach me! For free! I fear the results.