Yin & Yang
In the Qi Gong (Chinese) system I practice, the anterior or front of the body is where the Yin channels run. The posterior is where the Yang channels generally run. So in this system, the left is Yang, right is Yin which is the opposite of some other systems.
If something is Yin & Yang depends on different types of energy or 'Qi".
There are many different types of Qi (energy) in effect. For example, there is Qi related to the meridians and Qi related to blood. Both meridian Qi and blood Qi are two different types of energy. It's important to note in Chinese TCM, and other practices, the various forms of energy are commonly referred to as 'Qi.'
Left is considered Yang because blood flows out from the left side of the heart into the artery and goes back to the right side from the vein. (Blood follows Qi). Therefore Qi flows out the heart from the left and flows in from the right.
Emitting (giving) is Yang; Receiving is Yin. Because blood is flowing out or 'emitting' from the left side and 'receiving' on the right, this attributes 'yang' to the left side and the right as 'yin.'
Up=Yang (Rising) Heaven
Down=Yin (Descending) Earth
In other systems, the left is considered the divine feminine Yin or mother aspect, and the right side is the male Yang or father aspect. This system finds its foundation in the physiology of the female and male. The female 'receives' the male; the male emits into the female thus is the giver.
Other systems split the body into left-right, upper-lower switching Yin and Yang.
You can adapt and switch between any of the systems by understanding the principles of that system. For example, it is not uncommon in different forms of Qi Gong to switch hand placement; yin & yang elements for a particular aspect of the practice.
If you are doing energy work, using your intuition will guide you on which methodology to adopt at the time. There is no right or wrong.
Love & Light