Once XAMPP is installed you need to start it just as you did when you tested it.  You want the control panel.  Once that is running you need to start the Apache server.  You will also need the SQL server later if you do that tutorial.  You should not need the other servers.

XAMPP control panel

When Apache is running open your browser and type localhost as the address (if that doesn't work try 127.0.0.1).  You should see a Web page which welcomes you to XAMPP.  To get your own pages to appear on the server instead you need to do one of two things (the second one is recommended but harder):

Editing httpd.conf

You can access this from the XAMPP control panel by clicking on the Config button by Apache.  To tell it where your Web pages are you need to enter that location in this file (httpd.conf).  Look for DocumentRoot and change the two locations following this example but using your location (you can't have spaces in the names):

DocumentRoot "/Documents/web"
<Directory "/Documents/web">

The original version might have drive a drive letter but if your pages will be on the same drive as XAMPP you can leave the drive letter off (as shown).  This saves trouble if you ever move everything to another drive (or the drive letter changes for other reasons).  Note that the slashes are not backslashes.  Other than that the location can be copied from the location at the top of your Explorer window in Windows.

Now you can edit your HTML and PHP files, save them and the server will have the latest version immediately.

Be very aware that Apache will serve all files in that folder so don't put anything confidential in there.