> ## Documentation Index > Fetch the complete documentation index at: https://retain.so/docs/llms.txt > Use this file to discover all available pages before exploring further. # Start here > Retain helps you understand your customers through events and revenue data. ## Core concepts ### Events Events represent meaningful user actions that happen inside your product. Moments where users actually extract **value** from it, such as creating a project, scheduling an appointment, or sending an invoice. **Examples**: on Airbnb, booking a house is a meaningful event. On YouTube, it’s watching a video. On Spotify, it’s listening to a song. You get the idea. Placeholder: UI example showing an event being tracked (e.g. button click or action) ### Users Users are the people using your product. Each user has a unique ID that lets you follow their journey over time and understand their behavior. Placeholder: User profile card with avatar, name, and email ### Accounts Accounts are the organizations your users belong to. Essential for B2B products where behavior depends on company context. Placeholder: Company/account profile card with name and metadata ### Revenue (via payment providers) By connecting your payment provider, Retain automatically tracks billing events like subscriptions, renewals, upgrades, and cancellations, which combined with product usage data help you understand user behavior across the entire lifecycle. Placeholder: User profile card with avatar, name, and email ## Next step Connect your payment provider to sync your customers, MRR and churn metrics automatically.