Make a local port accessible from a remote server.

Make sure the server sshd_config have GatewayPorts yes

+--------------+    +--------------+
|localhost:4000|    |localhost:8080|
|local computer|->>-|vps server    |
|49.237.17.80  |    |34.80.255.217 |
+--------------+    +--------------+

ssh -R 8080:localhost:4000 user@34.80.255.217

The traffic on the vps server port 8080 will be forwarded to your local computer port 4000.

Access a remote port from local computer.

+--------------+    +--------------+
|localhost:4000|    |localhost:8080|
|local computer|-<<-|vps server    |
|49.237.17.80  |    |34.80.255.217 |
+--------------+    +--------------+

ssh -L 4000:localhost:8080 user@34.80.255.217

Tips

Adding the flag -nNT will not open a shell on the remote server.