Android <Service>

I 'm trying to connect Firebase Messaging Cloud.

Then,  I had to write <Service> in AndroidManifest.xml.

I'll look into <Service>, Today.

According to this site, <Service> is used to perform operations on the background such as playing music, handle network transactions, interacting content providers etc.  

https://www.javatpoint.com/android-service-tutorial#:~:text=Android%20service%20is%20a%20component,even%20if%20application%20is%20destroyed.

Also, the service runs in the background indefinitely even if application is destroyed.

FCM is need to run in the background, so it is a one of the services.