Navigating class

I can't navigate class when a button pressed given like this,

-(IBAction)menuBtn4id)sender;
{

Statistics *stati=[[Statistics alloc]initWithNibName:@"Statistics" bundle:nil];
[self.navigationController pushViewController:stati animated:YES];
}
Stratistics is UIviewController sub class.

Accessing Class Materials: Navigating Class Materials
When you enter the class (course) materials, the course table of contents will appear in the main screen area.
A top right navigation area lets you return to the table of contents (Contents), prepare and take a quiz (Take a Quiz), or pop up a PDF version of the core text material (Text).

A left navigation area gives you access to student features--syllabus, glossary, discussion groups, study guide. etc. The Study Guide includes chapter highlights, access to the self-quiz, and dynamic exercises that allow students to check their understanding of key terms and their definitions. Note that other Study Guide features differ from title to title.
The left navigation area also gives you access to educator features.

In the table of contents, clicking a chapter name will drop down a list of all the chapter's sections. Click on any one of the sections to enter the chapter at that point. You may click through a chapter linearly, using the forward and back arrows at the top right, or jump to specific chapters via this Contents screen.