I have just finished install postgres from the way that the postgresql website says for ubuntu20.04
when I run psql I get
psql: error: FATAL: database "myusername" does not exist
when I run createdb I get
createdb: error: database creation failed: ERROR: permission denied to create database
this is the one command that I have ran from looking online
sudo -u postgres createuser myusername
it seems to not have done anything though