How to rescue (on Photoshop) an underexposed ruined photo that I wish was normal?

How can I rescue (on Photoshop) an underexposed ruined photo that I wish was normal?

Added (1). It was taken outside in the late afternoon and the subject is darker than the natural/actual colors are. I'd like to rectify it as I like the composition.

If you have a raw format image (e.g. Canon.CRW/.CR2, Nikon.NEF, Sony.ARW, Adobe.DNG), the Camera Raw utility in Photoshop can help raise exposure in shadowy areas.

If you only have a JPEG, use an Exposure adjustment layer. This lets you set the increase in exposure, and limit what parts of the image are adjusted (via the layer mask). This won't completely save the picture, especially if it is a JPEG, since such areas only use a small portion of the total dynamic range available.

Should you need to shoot in a similar situation, learn how to use your camera's metering and exposure compensation features. Typically, you would use a center-weighted or spot metering mode to set exposure for your subject, and hold exposure while you re-compose for the scene you want. Some compact cameras have "backlight" adjustment. Flash can also be used to add light without overexposing bright areas.