eclipse rcp updates

For eclipse rcp applications, if we want to add a new feature and that needs to be installed through update manager, dont we need to create update site?

Request to clarify my following doubts.

1. c开发者_StackOverflow中文版heck for update means from where does the eclipse know that update is available? Is it from feature project? Feature project is creating new features to applicaton right?

http://wiki.eclipse.org/Equinox/p2/Adding_Self-Update_to_an_RCP_Application

http://www.ralfebert.de/blog/eclipsercp/p2_updates_tutorial/

These two examples show check for updates and install new software. what is here check for updates and Install new software?

Check for updates checks all known update sites for new versions of plugins and features, which are already installed in your application. With Install new software you can install new plugins (and specify new update sites).