How to run wordpress site, files from usb

Hello, I have recently taken my first programming project and it is with word press, I have never used it before as I have only done hard coding HTML/CSS before. My client has given me all of the files of her site, how do I run this on wordpress. I have installed wordpress and can run the test123 site but when I do the same thing on the local server with the info she gave me then I get a “Error establishing a database connection”. This is surprising because all of the file folders in the info she gave me is the same as the test site (obv the content is different). She was doing it on a mac and I am on windows but I assume that hsouldn’t matter. How can I fix this so I can see the site on wordpress and make the required changes that she wanted.

Thanks!

I tried changing the config file but that just gives me the setup again and not the site she has already made ??