So to simple explain a website with a forum (So you can see the difference
We will start at ROOT (/)
/ (This is root so the top level of a linux system)
/www/public_html/ (This is different from system to system but 99% of the time in public_html is where all your websites go. (I know for those that can say yes and bla bla bl but its ment as a simple guide) We also refeer to this as Domain root or Document Root
So lets say in this scenario you want to have a WEBSITE that looks fancy and all, and click on a link to get a forum.
/www/public_html/
In this folder goes all your files, some applications can have several thousand files. as @killshandra pointed out, might look similar but trust me they all do different things.
So we have a website lets say we a website consisting of the following files.
index.html
style.css
awesomeimage.png
So all these files goes then into your Document Root (/www/public_html) or / depending on the system. But for short i know it can be confusing but lets call it root.
So all good we have a website you go to yourdomain.com and you can see the website. NOW we want a forum so lets say we want to add it to community, so it will be in
yourdomain.com/community. To achive this we make a folder in root. so the structure now will look like this.
community
index.html
style.css
awesomeimage.png
All the forum files goes inside there so inside /community (This would then be /www/public_html/community) we might have something that looks like this
admin
uploads
public
index.php
conf_global.php
init.php
When you then visit yourdomain.com/community you will be presented with the forum. You can rename the /community to lets say /forum by just renaming the folder and visit /forum instead of /community.
Now lets say you DONT want a website you just want a forum, well then you just place all files inside the document root and when you visit yourdomain.com you will be presented with the forum..
I hope this gave a bit of perspective and might help you with what you where looking for.