How to subscribe a podcast available on Apple Podcast (https://podcasts.apple.com/...)?

The easiest way to find and subscribe to a podcast is to use the app search engine. But if for some reasons you don't find the podcast, you can paste its Apple podcast URL or its RSS feed url into the app to subscribe.
You can also use a service like getrssfeed.com to find a podcast RSS feed from different services such as Apple podcast, soundcloud, Google Podcast or even a blog.