EnterraHost
An alias is a second address that delivers to a mailbox you already have. A catch-all is one address that collects everything sent to your domain that does not match a real mailbox. They solve different problems and the second one has a cost worth understanding before you turn it on.
An alias is the one you usually want
Aliases let one mailbox answer to several addresses. info@, sales@ and accounts@ all arriving in one place, with no extra mailbox to pay for and no second password to manage.
Because it delivers to a real mailbox, an alias inherits everything that mailbox has, including its filtering and its archive. That is the whole appeal for a small business, the appearance of several addresses with the cost and the admin of one.
Aliases are set up on the mail service in the toolbox, alongside the mailboxes themselves. If you have not created a mailbox yet, creating your first mailbox comes first, because an alias needs somewhere to deliver to.
A catch-all collects the rest
A catch-all takes everything sent to your domain that is not already a mailbox or an alias. The usual reason to want one is that you would rather see a misaddressed message than have it bounce.
The reason to hesitate is that a catch-all accepts mail for addresses you never published, and a large share of what arrives that way is not from anyone who knows you. It is worth turning on when you have a real need for it, and worth leaving off otherwise.
If you do turn one on, watch it for the first week rather than assuming it is quiet.
What lives either side of this
Aliases and a catch-all are about addresses on a domain you already own. The domain itself is a separate job, and registering a domain covers getting one.
One thing this does not change is how your mail is filtered. Every mailbox here already carries spam and virus filtering, inbound and outbound, so creating an alias does not create a new place for unwanted mail to arrive unfiltered. If you run your own mail server instead of using our mailboxes, filtering is a different product entirely and Mail Protection is the one that sits in front of it.