A minimal configuration
MailerQ is configured via one central configuration file: "/etc/mailerq/config.txt". It holds many options. The most important ones are the address and login credentials of your RabbitMQ message broker and the address of your database. You probably need to change these settings. All other config file settings have decent defaults that work directly (although you might want to take a look at them later).
The "rabbitmq-address" setting in the config file holds the address of the RabbitMQ server that you want to use for message queueing. It has the format "amqp://user:password@hostname/vhost". The default value ("amqp://guest:guest@localhost/") works if your RabbitMQ server is running on the same machine as MailerQ, and when you've not altered the default guest/guest credentials.
If you have a cluster of RabbitMQ nodes, the hostname can be separated by semicolons (e.g. amqp://user:password@host1;host2;host3/vhost). Setting up a RabbitMQ cluster means you're less likely to lose messages when one RabbitMQ server fails.
MailerQ stores all runtime settings in a relational database. This can be a MySQL, MariaDB, PostgreSQL or SQLite3 database. The SQLite3 database is by far the easiest one to set up, because it does not require a database server and all you have to do is just enter the path to a file on your server where MailerQ can store its runtime settings. This file does not even have to exist as it will be automatically created by MailerQ when it is missing.
When MailerQ first connects to a database (or first opens the database file), it automatically creates all database tables and initializes everything.
To be able to connect, you do have to ensure that the appropriate database client libraries are installed on your system. If you use the sqlite database engine, make sure you have libsqlite3 on your system.