UNIX for Dummies Questions & Answers

ok thanks a lot for trying to help, you are awesome

So,
First of all, this is not part of my explaining just a notice:

I got 2 terminals in Application/Accessories - Root Terminal and Terminal. I use Root Terminal with line starting with
root@localhost, not Terminal that starts with leo@localhost

Explaining now:

/var/www/ is the place where I store wordpress files where I need to install wordpress, change files, run in browser. Owner of this file is: www-data ( right click in this directory says "you are not the owner, you can't change these permissions"). I think I created this owner with the commend I mentioned in first post
I download wordpress, put the directory in /var/www/ and start installation ( in browsers of course with localhost/wordpress, all of these are php scripts with interacting with previously created database)

Than I get to the part where wordpress says: Than I type this command:

Code:

chmod 777 /var/www/wordpress

and it installs smoothly.

Than at this moment, I need to install plugins or themes , and I get the picture I also showed in first post.
And I type this command:

Code:

chown -R www-data:www-data /var/www/wordpress

And I can install wordpress themes and plugins.

After that, I need to create folder in /var/www/wordpress/wp-content/themes/ and I can't make it. Right click in folder it shows: owner is www-data , "you are not the owner, you can't change these permissions". I change mod here: chmod 777 /var/www/wordpress/wp-content/themes and now I can make directory and write files.

That's step by step what I did. Maybe I shouldn't create www-data?