There you can see the rating of the show and also submit yours. In order to do this, you will be asked to listen to some episodes first. The rating is a simple 5 stars grade without reviews. Many shows don't have any rating yet as this is a relatively new feature on Spotify that started rolling out in mid-December.
The button is located on the podcast profile page under the description and shows a rating and its count.
Spotify: Music and Podcasts - Apps on Google Play
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