Need followup setup instructions to postgresql-10.3-1-linux-x64.run

Name: Sherman
Platform: HP Compaq 6710b
Operating System: Ubuntu 17.10 Fresh Install
postgresql: 10 Fresh Install. No other versions

What post-setup must I perform to get postgresql 10 running.

I used postgresql-10.3-1-linux-x64.run which ran great. It place postgresql
in /opt/PostgreSql. I am logged in as sql-dev the user I created when
installing Ubuntu.

Now I can't even recognize postgres. postgres has a system password and
sql-dev has a system password. I have to run all commands from
/opt/PostgreSQL/10/bin or such. postgres receives a password authentication
failed for user "postgres". Also for "sql-dev".

I have postgresql-10-A4.pdf but I haven't recognized what I need there yet.

Thank you;

Sherman