You can check your RHEL system and verify you have the package installed by opening a command prompt and typing:
[root@server ~]# service sshd status
sshd (pid 28104 5320 5318 5071 5069 1528) is running...
or check to see if it's even installed on your RHEL system:
[root@server ~]# rpm -qa | grep ssh
To start the service you can type:
[root@server ~]# service sshd start
Starting sshd: [ OK ]