Two handy examples:

1) Bind local port 4001 to port 5432 on postgres-server:

ssh user@postgres-server -L 4001:localhost:5432
psql -h 127.0.0.1 -p 4001

2) Bind local port 4001 to port 5432 on postgres-server using sentinel as a jump box:

ssh user@sentinel -L 4001:postgres-server:5432
psql -h 127.0.0.1 -p 4001