Adding updates/configs/changes, here's how it's done.

[weeksy]

So 1888 was asking about adding in a particular feature, there's 2 main ways of doing it on phpBB, this is one.

Firstly going into the Admin control panel. This is the back-end none of you ever see, but where all the configs are made/done.

mainboard by Steve Weeks, on Flickr

Then into postings, which allows us to add a new BB code

posting by Steve Weeks, on Flickr

Then create a new one
codes by Steve Weeks, on Flickr

and populate with the data from
https://www.phpbb.com/customise/db/bbcode/new_spoiler

added by Steve Weeks, on Flickr

As you can see, at the bottom we have a tickbox with either just enables the code so you can use the tags in brackets [spoil....] [/spoil..] or if you tick the box you get a button when you post

done by Steve Weeks, on Flickr

Then, the next time someone creates a post they have the ability to use whatever it is you've added, in this case, Spoilers.

spoiler by Steve Weeks, on Flickr

And that's it...

The 2nd method is a bit more complicate and means dragging and dropping files into specific folders on the operating system, then enabling, changing and configuring with the contol panel again. But this one started off as a complete mystery to me !