> 1. Is the Hbase snapshot take only pointer of table or it make copy of entire hbase table.
Within the cluster the snapshot is only an increase in metadata ('pointer' as you mention) where the HFiles carrying the data are not copied but are moved to a special location where they are kept for the life of the snapshot existing.
> 2. What export snapshot does in hbase.
Exporting a snapshot allows you to make an actual, full-data physical copy of the data to another storage/HBase cluster.
> 3. Is hbase snapshot allow in cloudera express version.
Snapshots by themselves are a feature offered by Apache HBase itself. It comes with your 100% Open Source CDH and is always available for use regardless of your Cloudera Manager version/edition. This would cover all the Snapshot information presented at
http://archive.cloudera.com/cdh5/cdh/5/hbase/book.html#ops.snapshotsWith Cloudera Manager Enterprise, however, you gain the additional abilities to schedule HBase Snapshots and schedule exports of these Snapshots to S3-compliant storages as described at
http://www.cloudera.com/documentation/enterprise/latest/topics/cm_bdr_managing_hbase_snapshots.htmlFor (1) and (2) I'd recommend reading also (in-full) the older but still relevant blog post of
https://blog.cloudera.com/blog/2013/03/introduction-to-apache-hbase-snapshots/