A reader account is free, and it's separate from being a writer here, even if you happen to be both.
When someone shares something with you, it shows up on your Home page and stays in your library whether you've opened it yet or not. A writer can share a single scene, a chapter, or a whole manuscript, either with your email address specifically or with anyone who has a reader account.
If a writer has turned on narration, you can listen to their book instead of reading it, chapter by chapter, in whichever voice they chose.
Reading itself has a few settings you can change anytime: a dark, light, or linen color scheme, a wider or narrower page, and larger or smaller text.
Discover shows a shelf of public domain classics available to any reader during the beta, along with a few authors you might not have come across yet. You can follow an author from their page, and My Library keeps everything shared with you in one place, with filters for what you've read, who it was shared with, and whether it's public domain.