Basically, the first machine (the feller-buncher) cuts down trees; a second machine, the skidder, drags the timber to a staging area; and a third machine, a tracked excavator with a grabber attachment, feeds the maw of a fourth machine, the horizontal grinder. The grinder shoots the chips into a semi-trailer.
Later in the day, two more tracked machines went over the ground to prepare for parking-lot work: a stump-grinder and a mulcher.
The feller-buncher looks similar to a trackhoe, but at the end of its boom it has a hydraulic attachment with a really big circular saw and a gripper. The operator rotates and tilts the attachment to align with a trunk or branch, and pushes in the saw blade. Using the gripper above the saw, he can hold on to the newly-cut section to set it into a pile, or can push it over to land on the other side.
Here's a view of the feller-buncher at work:
While the machine is capable of taking down a big tree with a single saw-cut, instead this operator took down big and even medium-sized trees one bite at a time. This avoids overloading the feller-buncher and saves the skidder operator a lot of time in gathering up the felled timber.
See this time-lapse of the feller-buncher, spanning less than an hour of equipment time: