Cannot see how to load any other games - except Reaper of Souls

Hi, I have bought the Eternal Collection of Diablo III

I have played reaper of souls until now, my question is how to do I load the other game versions I bought, Necromancer and Diablo III

Please help

They are all the one and the same. Once you buy the expansion thats the version you have to play.

So thats it, I have played the game…

Well there’s the campaign (which I hope you have done), and then adventure mode, which includes general farming, rifts and greater rifts (effectively dungeons).
There’s also a large number of difficulty settings so that you can increase / decrease difficulty to suit, but you are more likely to get better drops at higher difficulty levels.
So even if you have completed the campaign and reached level 70, there is actually still a lot more you can do.