Many Tai Chi postures have associated 'visualizations' to act as memory aids and assist you in 'picturing' the nature or character of these many and varied postures. These are only intended as a start point for your own imagination and creative thought to set flight.
The visualization given for 'Beginning', the first posture in motion is: "the lifting of the arms imitate the motion of the Sun rising slowly over the horizon".
If this works for you then that's good, but its only good if you really do 'experience' the nature and character of the posture. The visualization given is no more than a glimpse of an endless vista and the further you go the deeper it gets. None the less, its simple. The Sun comes up, the Sun goes down. The Moon comes up and the Moon goes down. That's it. The Sun does not come up to make the Moon go down!
The Ancient Taoist's of China called this "Wu Wei", mutual arising, no victor and no vanquished. Other translations and interpretations of Wu Wei suggest that this process operates on the micro and macro levels alike and can easily be personally experienced, acted upon and practiced in everyday life as "the action of non action". Like Tai Chi, this is done correctly when done 'effortlessly' and without expectation of gain.
The Ancients also suggested that the sequence of postures and the associated visualizations of any and all Tai Chi Form should never be written down, and even verbal or aural instructions avoided and be used only as a last resort. It was the common practice and accepted system of education (in Ancient Taoist Culture) that the student or apprentice absorb learning and understanding through the personal experience of repetition and the copying of acknowledged masters.
The student of art for instance, is shown a recognized masterpiece and the only instruction given is - copy this a thousand times! This process is seen reproduced in many religiously monastic and scholarly academic communities worldwide wherein text are copied or recited over and over, day in and day out. Thus I am inclined to urge students of Tai Chi: "Do this a thousand times and it will be yours".
The 'spirit' of Tai Chi that exists far beyond words and closer to visions. Tai Chi is riddled with 'visualizations'; there are thousands of them, but the only one that will work is yours. Try to not confuse the issue with words that mean nothing. Form begins where words and concepts end.