Paste a podcast RSS feed URL or an Apple Podcasts ID. This page lists the episodes whose publisher has attached an official transcript (the <podcast:transcript> tag from the Podcasting 2.0 standard), and lets you read or download them as text or SRT captions.
No transcript for an episode? Publisher transcripts are optional, so many shows don't have one.
A transcription tool that works from any audio file is coming soon (see the link below once it is live).