To add a new region server dynamically in a running cluster follow the following steps

1)Mention the ip address of new node on which new regionserver will run in the slaves file of the master

2)On the node make sure to have the hbase-site.xml configuration same as it is on other slave  nodes including master

3)Make sure to have master and new slave node clock syncronized elase you will get following exception Unhandled exception: org.apache.hadoop.hbase.ClockOutOfSyncException

After completing above steps start your region server by executing the command

$HBASE_HOME/bin/hbase-daemon.sh start regionserver

The number of region servers on UI of master node must increase,if region server started properly