The first is reading body language, the second would be controlling or altering your own body language.
(More specific “skills” such as exact behaviors or techniques you can actually use and put into action can be found in the linked articles below.)
Body language is directly linked with your emotional states. If you are feeling good, it shows through your body language, as well as if you are feeling bad. Also, if you consciously change your behaviors and posture from happy to sad, or from sad to happy, it alters your emotional state. You can read more about Confident/Insecure, Happy/Sad body language on the article: Confident vs. Insecure Body Language.
There are also certain behaviors that will almost instantly alter your emotional state into feeling happy and charismatic, see those at: 11 Happiness Triggers You Can Use Right Now.
Here are the two skills:
Honing down on these two skills will not only improve your everyday life, but also your whole life.