Nuclear fusion does not occur under the sort of conditions we are used to.  To fuse atoms requires special conditions.  Generally you need to be able to get the nuclei much closer together than normally occurs.

In the Sun this pressure is very high because of the immense gravity of the Sun.  The temperature is also very high.  Fusion happens at a nice steady rate.

On earth some of the methods of getting fusion attempt to do it by getting very high temperatures and pressures.

Inertial Confinement Fusion

In this method of getting fusion, a frozen pellet of Deuterium and Tritium is hit from many directions at once by very high energy beams.  Both lasers and particle beams have been used.  The outer surface of the little pellet is heated to millions of degrees and sublimes off at very high velocity, creating a rocket like thrust which compresses the inner parts of the pellet.  Fusion occurs.

Of course a lot of energy goes into the beams.  The hope is to be able to get even more energy out of the system from the fusion.  Although this system is still a long way from being commercial, there is some hope that it can be made to work and give us a lot of electricity.

Sources

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/finert.html

https://fusion.gat.com/icf/concept/