First things first, subscribing is free!
It is a convenience so that you don’t have to manually go looking for the show every time you want to hear it and/or know that a new episode is out.
Subscribing to a podcast enables you to keep up with all new episodes as soon as they are released. Regardless of which subscription method you chose to subscribe and listen through, the benefits are essentially the same. When you subscribe to a podcast you are notified when a new podcast episode is available to be listened to—either by streaming it or downloading it for later.
The primary method for subscribing is through a podcast app on a mobile phone.
Some podcast apps come as a standard download when you get a new phone while others may require you to download them through your app store.