For such a reaction to occur, the reacting nuclei need to have enough kinetic energy to overcome the repulsive electrostatic barrier between any two of them. For this to happen in laboratory experiments, the reacting particles need to be heated to very high temperatures, more than the temperature at the core of the sun. At such high temperatures, matter remains in plasma state, a collection of charged particles.
A Deuterium and a Tritium nucleus fuse to produce a Helium nucleus and a neutron. The reaction produces 17.6 MeV of energy, out of which the Helium carries 3.5 MeV and the neutron 14.1 MeV. In a plasma undergoing fusion, the reactions can be self sustained, as part of the kinetic energy of the resulting charged Helium can be used to maintain the very high temperatures required to sustain the fusion reactions.