Unable to trigger createdb

I have PostgreSQL installed on my computer and tried creating a database in the command prompt using the createdb method, but was presented with this error message: 

Nor was I able to delete said database:

Why is it that I have psql installed, and yet seem not to be able to use the various functions; is it a folder/extensions issue, or is there something else at play that I am not aware of?

Thank you,

Jack