Open app.guides.co anytime (menu → Reader).

You'll see:

• Continue reading - picks up where you left off
• Saved - guides you bookmarked (heart icon while reading)
• Your guides - things you authored in Studio
• Channel shelves - guides from portals and subscriptions you joined

While reading: use the table of contents, search in-page, and save guides you want to keep. Saved guides stay in your library even if you didn't write them.