error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement

I am new to the creation in C # . I do not know how to solve this problem . Can you help ? 56405-zrzut.jpg

A - B means nothing as you dont store the result.

C = A - B has a lot more meaning.

You mean to do velocity = new vector.

Or if you were trying to take away from the velocity you mean

velocity = velocity - new vector.

Try changing

GetComponent<Rigidbody2d>().velocity-=new Vector2(0, jumphight*time.deltatime);

Or

GetComponent<Rigidbody2d>().velocity-=new Vector2(0, jumphight)*time.deltatime;

Or Simply How meat5000 said

GetComponent<Rigidbody2d>().velocity-=new Vector2(0, jumphight);