core.atomic: atomicFence, atomicLoad, atomicStore

[ref2401 via Digitalmars-d-learn]

I learned how 'atomicOp' and 'cas' work and why i need them from 
the following sources:
http://ddili.org/ders/d.en/concurrency_shared.html (Ali's book)
http://www.informit.com/articles/article.aspx?p=1609144 (Andrei's 
book)

Can anybody tell me how 'atomicFence', 'atomicLoad' and 
'atomicStore' work and what do i need them for? Unfortunately 
official documentation didn't make it clear for me.