It seems that this sentence is difficult for us to understand. In fact, this sentence also confirms Laozi's philosophy, that is, the transformation of contradiction and opposition is an eternal law, and it is also Laozi's generalization of the laws of the world. We can read these two sentences in depth.
First of all, "the movement against the Tao" means that the opposite of contradiction is transformed into the opposite, which is always such a cyclical process. For example, if you practice Buddhism, you have to work hard towards something extraordinary, so that you can achieve the results you want and truly cultivate Buddhism.
"The weak use Tao" means that the function of Tao is invisible, but it is not negative, because Tao is the root of everything, and its function on everything is not so tough, but let it develop naturally, which is the "inaction" advocated by Taoism.
Just like our life, we must learn to be modest, think about whether our way is correct as an "opponent", put ourselves in the position of the "weak" to act, and follow the methods and laws of Tao in order to live freely. Laozi's sentence "Tao does what the weak do, and Tao uses it" mainly enlightens us that the transformation of contradiction and opposition is eternal.