Once you have completed calibration, you'll need to put the hotend on.
Get the hotend and the groovemount. If you're using the recommended JHead and their groovemount, it's a tight fit. You'll want to decide how you want the hotend to be oriented before putting the two together. If you have a resistor for heat, having the big heater hole aligned front to back and on the left side works best for me. If you have a ceramic heater cartridge, I'd have the hole running left/right, I think it's cool looking so I put it on the front. Whatever you like.
I use a pair of slipjoint pliers and press fit the hotend into the groovemount plate. I personally have the open end of the plate facing forward but I don't think it matters.
Once you get that in place, install into the bottom of the extruder. The hotend is a very tight fit - if it wobbles the print quality would be very bad. But it should be possible to hand press it in. Secure the left side with a 6-32 x 1" screw and a nut. On the right, secure it with the same, but install the fan mount, assembled with another screw in the hinge and two more holding the fan to it. The fan should blow towards the hotend.
For now, just make sure the wires aren't going to get caught in a belt or something. You're going to want to get started doing your first print. I really wouldn't try to finish up the build until after you print something. Do a few small prints first, get to know the machine. Then do a few more things:
- Bundle all the wires together sensibly. Use a bunch of zip ties, don't be shy.
- Screw down some of the provided anchor points at sensible places and tie the wire bundles to them. Make sure to secure them out of the path of any moving parts so they don't snag.
- Make sure that all wires going to moving parts have plenty of slack to move to their extreme positions, and that they don't have the possibility of flopping over/under/behind something during operations and getting caught.
- Use some wire bundling wrap and make things look nice. You want to be proud of this thing.
I've probably spent as much time fiddling with where the wires go as building printers in the first place. There's no right answer. You can look at the image gallery for ideas, but do what works best for you.