Hi @TakadaGuna,
at first: here is a great tutorial on how to install postgres on linux and how to create your first user + database.
If you are using REI3 on the same machine, you only have to enter port, name, user and password.
"host": "localhost",
"port": 5432,
"name": "mydb",
"user": "dbadmin",
"pass": "Pa$$w0rd"
(please dont't forget to rename the config_template.json to template.json)
Finally you only have to enable and start the REI3 service
