Multi Node Cluster Hadoop Setup
For your ssh problem just follow the link of single node cluster :
http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/
and yes, you need to specify the ip's of master and slave in conf file for that you can refer this url :http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-multi-node-cluster/
I hope this helps.
Try to create number of VM you want to add in your cluster.Make sure that those VM are having the same hadoop version .Figure out the IPs of each VM.you will find files named master and slaves in $HADOOP_HOME/conf mention the IP of VM to conf/master file which you want to treat as master and and do the same with conf/slaveswith slave nodes IP.
Make sure these nodes are having Passwordless-ssh connection.Format your namenode and then run start-all.sh.
Thanks,