There was an existing outlet that I recently removed, so I spliced the two wires together. I recently decided to add a new outlet in a different spot, so I added a long pigtail, connecting the 3 wires together with wire nuts, looking something like this:
There are many problems with the wiring and workmanship in the pictures:
At the outlet, Power (black) and Neutral (white) are wired on the same Neutral side of the outlet. This results in a short circuit through the tab between the two screw pads. Black goes on the other side of the outlet, where the shorter slots are.
Far too much wire stripped on the outlet connections. Even if the wires are attached on the correct sides of the outlet, the exposed lengths of copper can still cause a short circuit when the outlet is inserted into the box. There is usually a strip gauge stamped on the back of the outlet to show how much copper to expose. Shorten the exposed coper lengths per the gauge.
The wire at the outlet is wrapped the wrong way around the screws. The wire will tend to slide out from under the screw when wrapped counter-clockwise. Wrap the wire clockwise around the screw, and use a torque screwdriver to tighten the screws properly.
The wire nut for the black bundle in the junction box shows exposed copper, which indicates a possible too-loose wire nut, and may also cause short circuits with other box parts or wires.
This may be due to a temporary mock-up, but the cables going into the junction box need proper cable clamps applied to the box holes.
Respectfully, there is enough problem in this project to indicate that a licensed electrician needs to help you with this project to keep you safe. Things are not safe there now.
From the new pictures you have quite a few problems. Thanks for the pictures.
On the the outlet,first problem, black goes on the other side. Not doing so created a full blown short circuit. Second problem is too much bare wire on the screws.
Should only be enough bare wire to go around the screw itself. You have 4 to 5 times too much bare wire showing from the insulation.
There is stripping gauge on the back of outlet.
Third problem is the wires on the wrong side of the screw. The loop should be the same direction as the screw tightens.
There are no cable clamps holding the cable to the box. Should be 1/4 to 1/2 inch of outside cable insulation inside the box, plus six inches of the wires.
With the wire nuts should be no bare wire showing on the insulated wires.
You created a DEAD SHORT by wiring the hot and neutral to the same side of the outlet. No wonder why the breaker trips immediately.
I don't want to be mean, but this is a VERY basic mistake and you clearly need expert help. Like Triplefault said, there are a lot of other workmanship issues going on, I don't like to say this but every once in a while I do: Get a pro.