I have an outlet in a bedroom and want to add a couple more outlets in the room adjacent... I'll be running 12/2 wire for the new outlets the problem is that the outlet in going to tap into has two white and two black do I simply make two complete pig tails one for the exiting outlet one white one black and then the second pig tail for the new outlet?
I'm not sure I understand your proposed installation, but this is what you do, assuming the outlet is not switched in any way. I understand the two pairs of wire are both physically connected to the outlet. This sounds like a North American installation, I am assuming such, but instructions should apply to other areas, just that what each color does may vary. One pair is in coming power, the other continues on to feed other outlets or lights.
Remove all the wires from the outlet. Always connect all blacks together and all whites together (and bare grounds together). Each wire nut connection will have the two original wires, the new wire feeding new outlets, and a short pigtail wire. The pigtail is connected to the original outlet. Black wire connects to the yellow or brass colored screw side. The white connects to the silver colored screw side, usually marked as "neutral" (in North America).
I recommend properly binding the wire to the screws instead of using the convenient push-in connectors if you have a choice. IMO, you get a much more reliable connection this way, but the connection must be properly made up.
Don't use a larger or smaller gauge wire than the size used for the existing circuit. If the existing wire is #14 adding to it with #12 is not an advantage it's a disadvantage.
Always try to tap into a circuit where you're not going to overcrowd a box. 7 wires plus the receptacle is a code violation. And the reason will become apparent when you try to cram all of that into the box. If you found the last receptacle on the circuit it would only have 2 wires in it.