Zhan Zhuang is probably the most basic, simple but important exercise, fitting under the Qigong umbrella. It is an unusual exercise in that there is no movement, hence the name, ‘Standing Like a Tree.’ The focus is solely on breathing, relaxing, opening the energy channels through an upright and relaxed posture. It can be regarded as the purest form of mindfulness and standing meditation.
Visualisation often assists to understand concepts: Our feet sink beyond the surface, grounding us to the earth. They are the roots. Our legs and torso form the trunk of the tree. Our arms are the branches, with perhaps the fingers the leaves.
The primary purpose of Zhan Zhuang is to align the body to produce energy. We become aware of how out body holds itself, how dominant, strong muscles take on the work of weaker muscles, creating an imbalance and a disruption to the flow of energy (Qi)
For more information Zhan Zhuang and the Search of Wu is an interesting read.
Scott Jeffrey also has more details about Zhan Zhuang: https://scottjeffrey.com/zhan-zhuang