How to forceibly shut down a mac?
Press and hold the power button for several seconds and your Mac will power completely off. This should only be required in the most extreme circumstances. Normally, you should shut down your Mac by clicking on  the Apple icon in the upper left corner of the menu bar and selecting Shut Down... from the drop down menu.

Your applications are resuming when you log back in because you're telling OS X to restore their state when you shut down.

When you shut down or log out make sure the Reopen windows when logging back in option in the shut down window is UNCHECKED. Like this:

This will prevent OS X from saving the state of open applications and restoring them when you log back in.

You should also check your log in settings to make certain you aren't starting programs as login options. Open System Preferences and click on the 'Users &amp; Groups' icon. Find your name in the user list and click on it and then click the Login Items tab. Remove any applications you don't want to start on login from this list by selecting the application and clicking the - button at the bottom of the table. Like this: