A junction box is a standardized enclosed metal enclosure where conductors (wires) are connected together.
A junction box is a standard box that you will see along EMT or Rigjd pipe paths on the way from a panel to an outlet. There many standard sizes and shapes but one of the most common is a 4″x4″.
The purpose of the box is to separate the pipe runs into sections that won't have more than a total of 360 degrees of bends. Picture this: So there might be two 90s and a 3 point 30 degree saddle. That adds up to 270. But you notice you still have to make two more 90s before the destination. You could end where you are (if you can mount boxes there) otherwise I would move back one full pipe section where you would put a box fitting on the pipe where the coupling wasand you can attachh a bunch.
Now you can fish the pipe and pull wire through the first 90s to the junction. Pull all that you need to finish that run to the end receptacle . Fish the the remaining pipe and pull that wire to its final location
The reason you keep the total angle of sections of pipe under 360 is because after you hit tbat and try to fish it; it fails more often than not. If fishing was successful, pulling around 360 degrees worth of angles causes the tension to halt pulling like glue.