First read the readme_en.txt file in the xampp folder.
After starting Apache and MySQL in the XAMPP control Panel you would go to
http://localhost to test the XAMPP installation by selecting your language then exercising the demos and setting any security settings you wish to make in the left menu panel.
Then replace (delete) the 2 index files index.php and index.html in the htdocs folder with the index file and folders of your web site.
Then you once again type
http://localhost in the browser and you should now see your web site.
Once that is working correctly then try and use your LAN IP address from another PC on your LAN.
To access the XAMPP Welcome page again you would simply type in your browser:
http://localhost/xampp/index.phpLet me know please how you get on or if you get stuck at the next hurdle.
Good luck