I don't believe there is a relation between XAMPP and MQTT brocker.
XAMPP --> is like LAMP which is a web server - i haven't use it before so not sure what is its capabilities.
MQTT Brocker --> is a sw that work as server as messaging that have payload.
You need to install mosquitto Brocker on your PC - didn't try it bwfore on windows but i can see you can download it from:
	
		
			
			
				
				
					Source  mosquitto-2.0.22.tar.gz (GPG signature) Git source code repository (github.com)  Older downloads are available at https://mosquitto.org/files/ Binary Installation The binary packages listed be
				
				
			 
		 
	 
If you would like to link the mqtt messages to ur website/webserver, i am not sure how to do that, but a very good tool that i can recommend you research at is 
https://nodered.org which also provide a dashboard that you can use directly.