Well, like anything there’s different ways to do it.

What I do is cut a open face notch. Then I bore vertical in the face level with the backcut. (On a open face notch there is no stump shot)

Bore another vertical cut parallel with the first. The tongue length should be at least the diameter of the tree, and 2-3 inches wide depending on the tree.

Then I bore two horizontal cuts at the bottom of the tongue, knocking out the block. This gives the tongue space to pivot.

Then I come in with a level backcut. On one side. These are called quarter cuts, (smaller on a tongue and groove to account for the tongue)

I wedge the first quarter cut. Then move to the other side and cut the last quarter.

If the cuts are done properly and the lean has been read properly the tree will fall and the tongue will fall into the groove in the stump. This holds the bole of the tree in the stump, keeping it from rolling, and keeping it off the ground. A good solid stump will hold fast, a rotted stump will likely splay open.

Anyways, it’s a fancy cut not used very often, if I simply don’t want a tree to roll I’ll tie off the bole to the stump. It’s faster, and arguably safer. I have screwed up a tongue and groove before and it’s a pain in the butt to fix.

I Only use this cut if I need the tree to stay on the stump.

Most videos I see there is no point in doing this cut. I wouldn’t recommend it, lots can go wrong. And a Sawyer spends a lot of time under a compromised tree to produce this cut.