Entitlement management helps your support reps determine if
your customers are eligible for support.Milestones(Done in setup)
Milestones represent required, time-dependent steps in the support process.Entitlement Process(Done in setup)
Entitlement Process are customizable timelines that include all of the milestones that agents must complete to resolve a case and on time.

Entitlement(Done by creating a record in Entitlement object)
Entitlements tell the support team what service level each customer entitled to based on their SLA.

Lightning Milestones component displays all active and completed milestones on the case record page.
It has mark as completed link.
Show More and Show Less links are available to show more details and less details.

The completion date is set to future message will be shown on the Lightning Milestones Component if the Case Milestone completion date is set to future date time.

If Stopped check box is enabled on the Case, milestones time calculation will be stopped.
If Stopped check box is disabled again, it will start counting again from where it was left previously.

Entitlement Model	Description
Entitlements Only	Support reps verify that contacts are entitled to customer support before they create cases.
Service Contracts with Entitlements	Support reps verify that a customer is entitled to support based on a service contract.
Service Contracts with Contract Line Items and Entitlements	Support reps verify that a customer is entitled to support based on line items in a service contract.