Smart labels have a checkbox at the top-right which says:
Archive incoming Forums (skip the Inbox)
How about non-smart labels? How could I do the same. I couldn't find a checkbox on labels that I have personally created.
You need to change the filter which applies the label to those messages to also "Skip the Inbox (Archive it)".
If you want this to happen when you add the label manually, you probably want to use the "Move" action rather than the "Add Label" action. The former removes other labels on the message, including "Inbox".