PostgreSQL – Roles Without Linux Accounts

Basic question:

what I'm reading describes how to create linux users in parallel with postgresql roles.

However, I don't see the value in creating any of these users in linux – I just want to create a postgresql role – and login to that from my application – or when running psql from the terminal using my own login – but in the role of the project.

e.g. – if the project is 'foo' – I want to have the psql -U foo, but no 'foo' user under linux. After all – what's the point? It's a role purely for psql – not for linux.

Is this possible in Postgresql – and if so – how do I do this?

I've trivially created a postgresql user role – without a linux account – but then I cannot ever -U role, as I get an error around peer authentication.

So – I assume I need to change how postgresql is handling permissions – and that's where I'm too green with postgresql to know what I'm doing there.

Perhaps a pointer to a clear little document discussing authentication modes or connection modes and setup for postgresql would help me resolve my issues?