Hi Vandana,
There are a lot of resources in help.sap.com that help you find out the answers to your questions and umpteen number of posts and blogs in scn.sap.com that answer your question. This is just a brief response to your question and is not the complete answer and would suggest you to refer to help.sap.com for extensive knowledge.
SAP HANA - HANA also called High Performance Analytical Appliance (this full form is not used anymore). Its an Appliance because it comes with both Hardware and Software. Typically a database that stores data in-memory with a column based datastore. This is just a tip of the iceberg and you have great resources in help.sap.com and scn.sap.com
Native HANA - Harnessing the native capabilities of HANA such as its Modeler to build different Modeling objects or building applications would fall under Native HANA.
HANA Enterprise - HANA itself can be called HANA Enterprise (not used much), at this moment it is common to use the term Enterprise with HANA Enterprise Cloud which is one of the cloud offerings of SAP HANA
HANA Versions and SP - SP11 was released recently, and as far as which version is being used in companies that's a very broad question. Some might be even using SP 7 and and SP 8, it depends on when the implementation was done and what features they wanted to implement and whether they chose to upgrade or not
Read through the materials in help.sap.com and there are a lot of videos in the youtube channel SAP HANA Academy