simple example:
hostA - local server
hostB - remote server
In hostB, edit a '.rhosts' in HOME directory and the content is like this:
123.123.123.123 #IP of hostA
or
hostA #if IP exists in /etc/hosts
In hostA, try
#rsh hostB hostname #rsh [TARGET] [COMMAND]
#hostB
Then you get it!
man rsh to learn more!