You need BES for what you are trying to do. You need a blackberry data plan (either BES or BIS) to use any blackberry specific features such as push email, blackberry messgenger, etc.
If you are new to blackberrys, then you need to start out by reviewing the info on the FAQs to start with. Many of your questions will be answered there. Find the FAQs by looking at the menu bar at the top of each page on blackberrryforums.com. Click on BlackberryFAQ. Specifically, you may want to start with this one: What do I need a Data Plan for? - BlackBerryFAQ