To use an OPDS feed, you need a "client" app. Many popular readers support this out of the box: KyBook 3, MapleRead, YACReader (for comics).
This guide explores what OPDS feeds are, how they work, and why they are the "secret sauce" for personal digital libraries and public book distribution alike. What is an OPDS Feed? opds feed
The server hosts a collection of files (EPUB, PDF, etc.) and generates an XML file listing them. To use an OPDS feed, you need a "client" app