I can not understand how the Command pattern differs from Observer'a?

Question

Java

I have known the Observer pattern for a long time and just now I saw Command. And I did not see the difference in the fact that they do different things. The only difference between a command and an observer is that it contains the Involker(caller) class, which calls methods (commands) in the descendants of the command interface. I can not understand what is the essence of the Command template from the observer, when both do almost the same things? Could there be a difference in application?