Purchases is the client SDK for RevenueCat.
An entitlement represents features or content that a user is "entitled" to. Entitlements are unlocked by having an active subscription or making a one-time purchase. Many different products can unlock. Most subscription apps only have one entitlement, unlocking all premium features. However, if you had two tiers of content such as premium and premium_plus, you would have 2 entitlements. A common and simple setup example is one entitlement with identifier pro, one offering monthly, with one product. See this link for more info
Most well monetized subscription apps provide many different offerings to purchase an entitlement. These are usually associated with different durations i.e. an annual plan and a monthly plan. See this link for more info
Class containing all information regarding the purchaser
Entry point for Purchases. It should be instantiated as soon as your app has a unique user id for your user. This can be when a user logs in if you have accounts or on launch if you can generate a random user identifier. Make sure you follow the quickstart guide to setup your RevenueCat account.