From my understanding, Hbase is the Hadoop database and Hive is the data warehouse.
Hive allows to create tables and store data in it, you can also map your existing HBase tables to Hive and operate on them.
why we should use hbase if hive do all that? can we use hive by itself? I'm confused :(
So in simple terms, with hive you can fire SQL like queries (with some exceptions) on your table/s and is used in batch operation. While with hbase, you can do real time querying and is based on key value pair.
"why we should use hbase if hive do all that? can we use hive by itself" Because Hive doesn't supports updating your data set. So if you have large analytical processing application use Hive and if you have real time get/set/update request processing, use Hbase.