To be honest, the best way would be to work your way through the nodes and planets until you get to the Void. And the void is a place, not a thing - you can't have an orokin void, you can only go to or go from it.
If you want one fast, you can check the recruitment chat (I'd recommend the recruitment chat in Warframe as you should be able to find someone faster there, but you can try your luck here) and see if any one would taxi you there.
I recommend completing nodes simply for the fact you make more things available to you, like nodes with event missions like void fissures for opening relics, which will work towards new prime equipment for you.
Explore the wiki with the search bar above (denoted by the stylish magnifying glass within the page) any time you have a question and enter key words that would form topic entries such as 'void', 'relic', 'fissure', or 'mastery rank' - will save you and every one a lot of time.