求问point at,point to,point out有什么区别

eg：The teacher point at the blackboard and said:" Please look at these words carefully."Her mother says:" Do not point at the words when you are reading." point to:指向,指出；主要指的是比较远的地方.eg:He point to the house on the other side of the river and said:" That is my house." point out:给某人指出方向,药店,错误等eg:The teacher point out many mistakes in my homework.Please point out the man who saved the boy.