I've been told I need to set the permissions for everything in the htdocs folder to 777, but how do I go about doing this?
Thanks

'man chmod'

sorry, I don't understand that - what does that mean and where do I put that?

777 = everybody can execute and alter everything. That is for sure not what you want. However, it would go as follows (escaping like bash):
Better do the following (everybody can read, only owner can alter or execute):
If some cgi needs to write to some location beneath htdocs change ownership of those files/directories to the user used by your webserver to run cgis (normally apache, httpd oder nobody).

Put that into command line - it will display help about chmod command. Use "man find" to find out what above does in detail.

man is a build in technical manual. Simply enter man [command] to get details about any unix command. Of course, you need to know WHICH command.

chmod is the command to change permissions.

One thing about man: read the whole thing, particularly the last few lines. There you're see references to similar commands that may be helpful.

Okay thanks, I've got the man chmod and am now about to read it, but how do I find out where the file to change the htdocs permissions is?

htdocs is no single file but a folder. Ask the one who installed your system, he'll tell you. Maybe Have a look for /srv/www/htdocs , /var/www , /var/lib/apache/htdocs .

If you've installed the system yourself start reading the documentation coming with it - it will help you to actually understand what to do.