All of us possess different levels of calm. Some people are naturally born calmer, some people learn to be calm, and others can actively choose to have an attitude of calm.
Instead of trying to do lots of things at once, direct your energy into just one task at a time. This helps you focus, feel less overwhelmed, and slows down your mind so you can think before reacting.
There are certain things that will trigger uncalm reactions. In these moments there are lots of techniques to keep your calm. Breathing is always a fantastic tool for this, but everyone has their individual methods. Try different techniques to figure out what works best for you.