How do I access the Raspberry Pi file structure?

I’m running a Raspberry PI with Home Assistant installed on it. It boots fine and runs, and I can access Home Assistant. But I see people talking about making changes to the HA config files directly. Am I able to login to the Raspberry Pi itself? If so how do I do that.

Install the ‘Advanced SSH & Web Terminal’ add-on, or the ‘Samba’ add-on.