Its quite easy. Most telephones use only two wires. In older houses is a porcelain block with wires coming from the street poles. The internal wiring connects to this block. Newer homes have a bridge interface. Outside on the house is the trunk connector. I'll try to draw up something that looks like these.
Essentially the red and green wires, the middle two wires connect to the phone through the modular connector and the jack.
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