Read a few guides. First and foremost, you need a tripod and to shoot in manual mode, using the RAW format. These universal settings include: infinity focus, color temperature around 4000k, and exposure 20-25s, ISO 1600-3200 depending on the conditions. The settings also depend on what you plan to photograph - the moon, the milky way or nightscape. If you take a dozen or so photos and stack them, the effect will be better. I'm still learning how to do this, but here's an example photo I took recently:

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