Assuming you have cloned OpenCog repository in the
~/src/opencog folder of your home directory, and that you have successfully built it inside
~/src/opencog/build, in a new terminal window run
cd ~/src/opencog/build ./opencog/cogserver/server/cogserver -c ../lib/development.conf
This loads the CogServer with the development configuration file development.conf.
You should see the following output by default
Listening on port 17001 ... ...