Rather Newish to OOP, Controller question

Let me try again at explaining what I am trying to do here:

Controller Project -> Class Project -> Method Join($project_id) -> View join with the above code. Once that page is loaded the visitor is asked if they would like to join the project. If they click join:

Controller Project -> Class Project -> Method Enter($project_id) -> View join is called and the code inside Method Enter is run.

What I am trying to figure out is if this is the best way to do this because I want to also do the following:

1) Prevent direct access to Method Enter via url. So if someone copies the url http://www.site.com/project/enter/1 into their browser it will not run any of the code within the method.
2) Provide error checking and error feedback after the Join button is pressed as well as provide information about things that may have changed due to them joining the project (ex. list how many more projects they can now join, return an error if they are not allowed to join, return an error if the project became full or expired before they pressed join... etc)

Is this approach with MVC the correct one so far? I apologize if this is a question that should be easy to figure out via documentation. It just isn't clicking to me and my MVC learning curve still leaves a lot to be desired.