JWST lifted off from ELA-3 at the Guiana Space Centre. The launch took place on 25 December 2021 aboard an Ariane 5 ECA rocket, in flight VA256.
ELA-3, or Ensemble de Lancement Ariane 3, was built for Ariane 5 launches at Europe's spaceport in Kourou, French Guiana. Its location near the equator helps rockets gain extra speed from Earth's rotation, an advantage for missions requiring substantial launch energy.
The other choices point to different facilities or launch providers. LC-39A is a famous Kennedy Space Center pad used by NASA's Apollo missions and later SpaceX; SLC-40 is another SpaceX facility. ELA-2 was an earlier Ariane launch complex at Kourou, but it was not the pad used for Webb.
The Ariane 5 launch was unusually precise. That accuracy reduced the amount of propellant Webb needed for later course corrections on its journey toward the Sun–Earth L2 region.