If you’re interested in trying tai chi, you need a teacher, there is no way you can effectively learn tai chi on your own from a video.
Find a teacher who offers classes that will allow you to study for an extended period of time. A solid foundation of basic tai chi skill takes about a year to build.
Although you will notice improvements in balance and coordination after a few months of taking weekly classes, you will experience many more health benefits the longer you study and practice tai chi.