The psql command is a client - an "interactive terminal". It provides a command-line version of pgAdmin.

See here for other client applications:

https://www.postgresql.org/docs/10/static/reference-client.html

The "create extension..." command is one that you give to either psql or pgAdmin; they execute it against the current database.

hello again I have a small problem here can someone tell me briefly how to do it? I am getting this error 

When I give ant fresh_install it gives error PostgreSQL 'pgcrypto' extension installed /up to date? False (not installed) Create extension pgcrypto.

I have tried to look up for solutions and they all say I have to run a command 

# Login to your "dspace" database as a superuser

psql --username=postgres dspace

# Enable the pgcrypto extension on this database

CREATE EXTENSION pgcrypto;

 but where I got confused is from where do I run these commands.is it from cmd? or in pgadmin query tool? I need clearly articulated  steps