what is gora? what does it do for us? how it work with hbase? which features dose it have? do you know a good essay or web page which can help me?
From its incubator page on Apache.org:
Gora is an ORM framework for column stores such as Apache HBase and Apache Cassandra with a specific focus on Hadoop.
Gora has not made any public releases yet, so you'd be a brave man to use it for a project aimed at production in the short/medium term. However, there is quite a bit of material in the pages linked above, including a tutorial page.