new installation using old SQL and WP files

Hi guys
I am new to here and new to WP, I need your help, so thank you in advance.

I had done a wp installation and changes to the theme, and have got a database copy and the whole public html folder files.

The client got his family friend to do a some thing to the website (i believe a new installation)

Now what I wanted to do is upload the files to the folder using FTP, which I did, but I got an error by visiting the link. So I am not sure if I should import the Database file first or upload the files using FTP, or should I first of all install a fresh WP and then upload the files then import the DB?

This is where I need help please, thank you everyone in advance.