Hello, Jasmin, & welcome. My first question is–did they give you the database file also, or, barring that, exported content files in .xml format?
You’ll need to install files to the web root folder of whatever you’re using for your local server. In many all-in-1 solutions, ie, Xampp, etc, that is the htdocs folder. I usually install to a separate folder underneath the web root, ie, wordpress, just so I can have more than 1 CMS on the local server if I want that.
You’ll also need to create a database, likely using PhpMyadmin, & then import your database into the 1 you just created. Make certain the database user you choose or create has all privileges on the database. Don’t forget to change the wp-config.php file to reflect those changes.
I next use a search & replace script to change the domain to the localhost install, ie, search for https://www.sitename.com & replace it w/localhost/wordpress. You may find it necessary to do that a couple times to catch all iterations of urls, ie, https://sitename.com, etc. I personally use a search & replace plugin by Interconnect/it, but there are others out there as well, & Google is your friend. The 1 I mentioned specifically is at:
https://interconnectit.com
You may also find it helpful to use a plugin for this purpose, such as Duplicator, found at:
https://www.ads-software.com/plugins/duplicator/
(this is not an endorsement, & there are others, w/which Google can help). It may eliminate the need for the search-&-replace script.
Hopefully this gives you a few ideas, but don’t hesitate to write if you need more help.