New to Zen and taking on existing site

I am very experienced with HTML and have always built my own websites and have a multi domain hosting
A friend asked me if I could host her domain name and site. I accepted thinking it would be a simple matter of transferring files from one site to the other.
Well being so unfamiliar with Zen cart I'm not sure if I have taken on more than I can chew.
Her last hostinf provider made all of the files available to me and I FTP'd them all to httpdocs on the new domain.
Now that the Domain name has also been transferred to my hosting provider I thought things would be fairly simple but I have to be honest and say I'm a little lost
aparrently the index.php is pointing to the previous hosting provider and I'm not sure what to do next.
I've aquired the book e-start your own web store and spent all weekend reading from it. Its very helpful from the point of view of building a site for the first time. But from my point of view at the moment I feel like I would if I were flying an aeroplane for the first time without an instructor.

I'm sure it will all make sense as I move on with it but I just feel the need to be pointed in the right direction.
So any help on this would be greatly apreciated
Thanks

1. even though the domain has been transfered have you confirmed that it is pointing to where it is supposed to be (nameservers)? and how much time has passed for dns propogation?

2. Have you adjust the 2 config files to reflect the changes between the 2 hosts? includes/configure.php and admin/includes/configure.php

This sounds most likely to be a classic configure file issue. There's a helpful FAQ about transferring sites. Note in particular the bit about the database, as you don't mention this in your original post.