Just like the title how do they dub it? Do they actually watch a clip of the character there gonna be voicing or just receive a script like how actors do it.
And Also how do Funimation make the english endings/openings for some of the songs do they receive an instrumental version or just edit out the voices of the full song?

I guess it would depend on the director. Some may require people to watch the original version while some may not require it. I would imagine that most would have them watch the original just to see on how they should act the part even though the way the ultimately act depends on what the director tells them to do. I read that each dub episode takes $10, 000 to actually dub but I don't know for which company that is nor do I know if it is official or not.

As for how they do the openings, I imagine that they would get an instrumental of the actual piece and just add vocals over it. There's would be no reason to get the actual song and spend time having to edit out the voices if they could simply get the instrumental.

If I remember correctly when watching some of those BEHIND THE SCENES Extra DVD stuff basically yeah I believe they get an idea of how the character was originally potrayed then they act and do their impression.. then the director reviews and they go from there.