We have did the canal twice, (Doing it again full transit in four weeks though), once partial transit and the other all the way through. I imagine the partial transit experience varies from line to line. We did it with Princess. We went from east to west. On the partial transit you do only one set of the three canal locks that allow passage from ocean to ocean, the easternmost or Atlantic locks are the Gatun Locks. (Three sets of locks -- Miraflores, Pedro Miguel, and Gatun (from the Pacific to Atlantic) -- are included in the canal).
The Gatun Locks lift ships in increments, one lock at a time until they go from sea level to 85 feet above sea level at Gatun Lake. Once in Gatun Lake the ship didn't anchor but we were transferred to shore on tenders where we boarded a bus which took us back to the Gatun Locks where they provided us with a detailed land tour of the locks and their operations. After that, on the bus again, they gave us a tour of the new eastern locks still under construction at that time. Afterward they took us to the nearby railroad where we boarded a deluxe observation car on a train which took us to Panama City. After touring Panama City we boarded buses for a return to Colon where we boarded our ship again.
Once the ship is in Lake Gatun, you have the option to stay on the ship, or take a tender, like we did, to catch a tour. If you don't have a tour booked, you can't get off the ship in Lake Gatun. The ship will sit in the lake for a while, and then turn around, and go back down through the locks, and dock in Colon where it waited for those of us who took day tours to the Pacific Coast.
We really enjoyed both voyages at the canal. Truthfully, if you took a partial transit like we did you see and learn a lot more than when doing the full ocean to ocean transit.