General question about ftp

Hi guys,
This is just a general question, as I've been having a lot of problems with plugins causing errors. So, WPMU Dev and many other plugin developers have taken time to help me and I am most appreciative!!
Heres' my question about that:
Whenever I get help from a developer, they usually ask for my ftp information.
But when I set up an ftp account, it goes to an ftp folder and not directly to public/html~~WP. I can't change the upload path via cPanel. So whenever I ftp to my account, I then go into my cPanel and drag the folder to where it needs to be in the public folder.
So... whenever I give a developer the ftp info so they can help me, they always tell me they can't access the WP folder.
Can someone kindly explain the process to me when a developer goes on my server?
Can't I just give them my cPanel or wp-admin login info to get the job done? I can't figure out how to have someone else properly ftp into my server. It's a VPS so there's no hosting provider?
Thanks to anyone who can break this down for me so I can understand it. Apparently, I'm doing something wrong?
--hg