I have no real firsthand experience making syrup, but one of my scout leaders years ago used to make his own so I picked up some bits and pieces from him.

When it comes out of the tree, it's very watery, I've never had the chance to try it myself but I'm told that it's very refreshing, and I believe it's actually lower in sugar than something like coconut water.

Then you boil it down to concentrate it into a syrup.

And as I understand it, that's pretty much it, I suspect at some point it maybe goes through a sieve or a filter of some kind to catch any particulates that might be in there.

I don't know if it's a common practice, but my scout leader had also rigged up a reverse osmosis system to cut down on how long he needed to boil it. Normally with a RO system, it puts out clean water and you throw away the concentrated waste product, but in his case the "waste" is what he wants, not quite syrup, but more concentrated maple water that requires less boiling to make syrup.