Take your other characters as group members

One guy i met took his monk which was another one of his characters he created as part of the group? how do i do this?

If you're saying he had two of his characters in the same party then he probably has 2 accounts with two computers, right next to each other. If not that, then it was probably something against the EULA.

Why didn't you ask him how he did it?

he was sitting right next to me but when i finished the quest with him he said he had to go and ran out the door....
in the part box it had his name then his other character's name below his but indented
Example:

Kingsnake ss
Him
(indent)his other guy
4th member

that is a hero
they come with GW nightfall. and are basically henchmen

so i have to buy gw nightfall before i can do that, or can i buy any expansion pack?

There is no expansion pack, only stand-alone games and Nightfall, aka Elona, is the one with Heroes.

Yes, you'd have to buy Nightfall for heros. And you have to work your way throught the Nightfall story line to get them all. (The monks come pretty early in the game. And when you do, you can have up to 3 of your heros in the party. A second player can add 3 of his/hers as well.