Tai chi is often difficult to learn. Every position is given in detail by the teacher to the student. Arms and legs, the body, and then other aspects, such as the gaze. The fine tuning of tai chi postures takes many years, and in a sense will never end.
Tuning up? Like a car or an orchestra, fine tuning (and tempo) is the aim of anybody who wants to improve.
The human body is like an orchestra in tai chi. The upper body, particularly the arms, is light and flows, like the strings (violins, treble clef, piano right hand). The lower body, the legs, is a like the bass (continuo, bass clef, piano left hand) where is there is less movement and a more solid feel. The waist joins the two, and corresponds to the conductor, telling each instrument what to do! When the tai chi postures are controlled the waist, the whole orchestra works together, in perfect harmony.... a symphony of movement.
The starting posture in tai chi (taiji) is that of complete stillness, which represents the "tao". The "tao" is the "uncarved block" and the movements in the tai chi set are the interplay between Yin and Yang. At the end, we return to stillness. This pattern is like the life of the Universe, which also started from the Void. It is an open question in cosmology is the Universe will contract back and end in a "Big Crunch".