ultra-n00b AG question

OK so this may sound extraordinarily dense, so I apologize.

Here's my totally inexperienced reductionist understanding of how all-grain brewing works:

Hot water is introduced into a vessel which also contains malted barley and that water/ grain becomes the mash. This water remains in the mash and the temperature is held steady during this process for a preset period of time (depending on the recipe). The end product is wort.

When that that period of time is over, the wort is drained out of the Mash tun and recirculated. The purpose of the recirculation is for the mash to act as a filter for the wort.

[This next part is what I have questions about, and I'm purposely ignoring Partigyling. I'm also focusing on fly sparging, for simplicity.]

After recirculation, this wort is drained from the MLT and into the boil kettle. When about an inch of wort remains above the drain bed, sparge water is introduced into the same vessel the wort was just drained from. An equivalent amount of sparge water is used as the volume of wort which has been drained before it.

As this sparge water is being introduced, the MLT is still being continually drained into the boil kettle.

As soon as the requisite amount of wort is created through this Mashing/ Lautering process, everything else about the brewing process is identical as extract brewing.

Is my understanding of this process correct?

You pretty much have it.

The sparge water volume will vary depending on how efficiently you've extracted the sugars from the mash. the less efficient your setup is, the more you'll need to "rinse" those grains and the more preboil volume you'll have.

Oh...and make sure those grains are crushed...

Yes, basically. When you fly sparge, though, most people do a mash out, not just drain it. You want to stop the conversion process and stop the enyzmes from continuing to work on the wort. You want to hold the "profile", so to speak.
So, you'd wait the 60 minutes for the mash to convert. Then, introduce some boiling water to bring the entire mash/grain mix up to 168 degrees, and then drain, recirculate, and begin to fly sparge.

I batch sparge, so I don't do a mash out usually. I drain my MLT, then add 181 degree water (or whatever my calcuations come out to be) to my drained grain bed to bring the sparge temperature to 168. I stir that, vorlauf (recirculate) and then drain it and do it again with 170 degree water. (The second time, the grain bed is already at 168, so I don't have to add as hot as water. I split my sparge water into two batches.

If you're fly sparging, you are correct that you want to drain as slowly as you add water to the MLT. This should take from 45 minutes to an hour.

That is probably the best, simplest and most succinct description of AG brewing I have ever seen...er, read.

You nailed it on the first try.

Save it for whenever another noob asks the very same question (like tomorrow probably)

Good job