Dual shutter buttons in camera app

Pick the top one and merge it with bottom

That's floating shutter button.

Drag it back and merge it to the main camera shutter button or long press and delete it.

Hold the upper shutter button then move it by swiping and place on the lower button and they'll merge into single button at lower end

If you visit the settings under the camera app, you'll see an option for floating shutter button. Please deactivate it if you don't want the extra button.
The use of this is to take photos in case your finger can't reach the fixed shutter button. You can adjust the position of the floating shutter button as per your requirement.