The coils are wound on a form then the ends are taped to hold the shape. all coils are the same on a three phase motor. the slots have formed insulation inserted in them then the coils are laid in . The slot caps are inserted after the coils are all in place , the inter connections and leads are installed and tested for faults. then the stator is dipped in hot varnish that impregnaters the wires and coils locking the whole assembly into a solid mass.
note that there are usually more than one coil in a slot and that an interwinding insulation barrier is needed.
These single phase slot holes may not be large enough to accommodate all the wire and insulation required for conversion to 3 ph. In addition you still must address the rotor issue.

This is not from hands on experience as I have never done a motor, but I have rewound a number of generators on weekends at my rewinders shop when we needed them faster than his workload could allow. I have seen the entire process through for motors and generators up to 400 mw. it is interesting but very repetitive and would soon become boring at least for me