Queues are optional, however when enabled they will increase the performance of your application. Tasks that would take a longer time to complete will be automatically added to background "queue" so your application can continue to run. For example, when sending an email to user, "email sent" notification can be shown to user instantly, instead of them having to wait until email is actually sent out, which can take several seconds.
There are several available methods for queue. Active method can be changed from admin → settings → queue page.
Sync - Default queue method, disables queue.
Beanstalkd - Beanstalkd will need to be installed and running on your server in order to use this method.
Redis - Recommended option. Redis will need to be installed and running on your server in order to use this method.
SQS - (Amazon simple queue service) Cloud Based queue method. You will need to register for an account and enter your credentials into settings page.