Let’s say, a user1 has a ssh connection to the ssh.exampleserver.com, and he would like to view a webpage on intranet server 10.0.0.11 available from exampleserver.
Then command could be like this:
ssh -L 8000:10.0.0.11:80 firstname.lastname@example.org
If using Putty, one would have to do add at Connections/SSH/Tunnels (source port 8000, destination 10.0.0.11:80)
Now user1 can see the webpage in browser at localhost:8000 .
There are nice articles covering this topic, like SSH Tunnel – Local and Remote Port Forwarding Explained with Examples, or SSH Port Tunneling with Putty.