On this page of the Biomutant game guide you will learn if it's possible to aim accurately with guns, i.e. to zoom in the camera and optionally use the crosshair. This can be an important matter if you are planning to fight at range often.
While playing Biomutant , you may be surprised to learn that the L2 button / left trigger on the pad is not used to aim your gun, as opposed to almost all other games of this type.
Instead, pressing and holding the L2 button displays ability icons in the game, which are assigned to the four main pad buttons. This allows you to easily activate a memorized skill.
In Biomutant , there is no option to accurately aim with guns. Instead, you just have to immediately start pressing the R2 button / right trigger to fire. Bullets will fly in the direction of the camera, so you need use the right analog stick to aim. Watch your opponent's health bar (above their head or at the top of the screen in the case of bosses and mini-bosses) to make sure your attacks are effective.
A similar restriction applies to other ranged weapons that aren't guns, such as the boomerang pictured in the image above. You must face the exact direction of the opponent you want to hit. Otherwise, a ranged attack may end in a miss.