Understand Guitar Wiring Diagrams
Now here are two diagrams of the exact same schematic. Both diagrams show exactly how to wire a one pickup, one volume pot guitar. The left side diagram shows how ground networks are often shown in guitar wiring diagrams, with implied knowledge. Many guitar wiring diagrams assume that you know where to wire the ground wires and often just show the positive wires because it is easier to visualize the path of the audio signal. The general rule of thumb for grounding is that if you see those grounding symbols (the antenna-looking symbols in the left side diagram) then it should be a ground wire which goes to the case of the volume pot. This is what the green wires demonstrate in the right side diagram.