For easier aim, check if your aim assist mode is turned on. Aim assist is usually required for those who have a touchscreen phone and uses a touchscreen to aim accurately like you are using a mouse to aim.
PUBG usually marks random regions as red zones and whenever you find yourself in it, it is highly suggested to get out of it as fast as you could or else you might get stuck during an airstrike and will kill you. Unfortunately, getting out is not that easy, hence, to survive, we recommend that you go inside a building.
In the settings cog, found on the top right, go to basic and click on Peek & Fire. This setting will allow you to peek from any behind cover and lets you shoot without having to expose yourself. This setting will still expose your head. Thus, you will still need to be cautious.