What does purge the cache actually mean?
A: What that does is it deletes all the "cached" files (copies) from the server.
phpbb3 makes a copy of every single file that has been accessed on your board.
The purpose is to make accessing the files used the most, faster for the user.
What it mainly does is confuse people, especially when trying to make edits to the board files.
Any time you make an edit, you have to clear/purge the cache afterwards to see the changes.
If you are going to be making a lot of changes to the files, then you can make a change in your admin panel to solve the problem.
In the admin panel:
On the left menu , find "load settings" at the bottom.
click on that.
On the right side, find: "Recompile stale style components:"
set that to yes
Click submit.
On the main page of the admin panel, purge the cache again.
Now, any changes you make to the files will show up immediately after refreshing your browser without having to purge the cache every time.

