The Triple Alpha Process is a Fusion reaction in stars turning Helium into Carbon. This happens in older stars with abundant helium when the core collapses to produce sufficient heat. Helium fuses into Beryllium-8 which then fuses with another helium atom to produce carbon.

4    4     8
 He + He -> Be (-93.7keV)
2    2     4

8    4     12
 Be + He ->  C (+7.367 MeV)
4    2      6

At about 100,000,000K, helium fuses faster than beryllium-8 decays and this process progresses. After this, some Carbon and Helium can fuse into Oxygen.