I cannot charge my iPhone 12, no charger in box

See the following from Buy iPhone 12 and iPhone 12 mini - Apple

As part of our efforts to reach our environmental goals, iPhone 12 and iPhone 12 mini do not include a power adapter or EarPods. Included in the box is a USB‑C to Lightning cable that supports fast charging and is compatible with USB‑C power adapters and computer ports.

We encourage you to re‑use your current USB‑A to Lightning cables, power adapters, and headphones which are compatible with these iPhone models. But if you need any new Apple power adapters or headphones, they are available for purchase.

If you don't have a cable and power adapter from an older device, one option is to use the following with the new cable: Buy 20W USB-C Power Adapter - Apple

You purchase a charger if you don't already have one.