ADD is pretty much like. . .oh. . .say you have a TV that usually works semi-okay, but it has this quirk. It changes channels randomly.
You'll be half-way through a show you really wanted to watch and boom! The channel changes to another show.
Or you'll be sitting there, trying to watch the news, and the channel changes. For all of 10 seconds. Then it changes again. And again. And again.
That's kinda' sort of what ADD is like, at least for me. It's not that I don't want to pay attention - in fact, what's in front of me may be enthralling - but the channel of my attention just switches. It just does. And it may switch and switch and switch or it may not.
Conversely, sometimes, I simply CAN'T change the channel. I remain fixated on one channel and stay on it. Nothing else penetrates: I'm focused only on that one channel.
Now, I know coping strategies. I know to have 2 or 3 or 4 things on my plate to work on at any one time. Then when my mind swaps channels, generally, it's on one of the OTHER things I want to work on, and not something totally random and pointless. I know to swap channels even when I'm on a channel (topic of thought) that is really interesting, so that I don't go all single-minded for hours on end. I know to always have the radio on news or something involved that requires some sort of thinking, just so that I do have 2 thoughts going at all times. Strangely, this keeps me focused on the road.
To-Do lists are good, especially ones I can post and see. Then when I'm in the middle of changing, I have something tangible to direct me - focus on this, not that!
Anyway, that's ADD. Best explanation I can find for what it's like.