These have got three main uses:
1. levering trees with a slight back lean so you can put them down in the direction you want, not the direction they’re leaning.
2. Rolling a hung up tree off the tree it’s hung on (using the hook on the side)
3. Rolling logs on the ground.
For levering down trees, do a split level cut where the back cut is halfway through the tree. Insert the felling lever, then cut the other side of the back cut, dipping nose of the bar just below the lever so the chain clears it. Once the saw is clear, if the tree doesn’t drop, give it a push with the lever.

Cutting the second part of the back cut

Stump showing the two cuts, with the lever still in position