Y'know how hard it is to get an electrician here in the neighborhood? Well, this crew started out with some heavy-duty do-it-yourself repairs to make on the Skylab that had been badly damaged during launch.
This mission was officially designated Skylab 2 (Skylab 1 was the launch of the station itself), but it was almost universally referred to as Skylab I (with a Roman Numeral). The human missions were launched atop the Saturn 1B launch vehicles.
The unscreen/meteorite shield had torn off during launch, taking with it one of the two solar panels and badly damaging the other, which would not deploy. The crew's first priority was to fashion some kind of sunshield, because the high temperatures threatened to spoil the food supply and made the interior of the station too hot to occupy, as well as releasing toxic gases from the plastics on-board and ruin all the photographic film. While staying in the more pleasant Apollo Command Module, they made a "parasol" out of foil to shield the Skylab from the sunlight, and the temperature dropped enough that they were able to enter.
Two weeks later they performed a space walk and freed the damaged solar panel, which finally gave the station electrical power, and Skylab was in business! For the remainder of their month-long stay, the astronauts performed other handyman chores, conducted many medical experiments and took over 29,000 pictures.
This mission more than doubled the previous American space endurance record set by the Gemini 7 astronauts.