What do the internal space and external space of characters mean in calligraphy?

Internal space is the structural problem of the word itself, such as your word, which is the left and right structure. When writing, pay attention to the grasp of the distance between the left hand and the right hand. External space means that the spacing between words should be just right. In this respect, you should watch more videos of calligraphy lectures, and realize the true meaning from them. Calligraphy depends on itself most of the time, really.