Congrats on joining the cook kids club lol. Now to something more serious, helping you turn on flashlight for iPhone 12. The process is pretty easy.
Use your finger and swipe down from the top of the screen (top right to be exact) and then in the middle of the screen look for the flashlight icon. Select it to turn on iPhone 12 flashlight. When you want to turn off flashlight on iPhone 12, do the same process and just select on the flashlight again to turn it off.
You are correct, when you rotate your iPhone it is suppose to switch from vertical to horizontal. I’m guessing the issue you are having is that you have the iPhone 12 rotation lock enabled.
It simple to disable and go back to normal though. All you need to do is go to the Control Center. You can do this by swiping down from the corner of the screen (right hand side). Near the middle of the screen you will see a “Lock” button. Tap on it to turn off Auto Lock.
Then try to rotate screen of iPhone again and it should solve your problem.