Companies and HR teams will provide a specific number of paid holidays as leave entitlement for employees.
Employees then can book or request holidays. HR teams or team managers can review such requests and approve or deny them based on business needs.
Such a process gets its level of complexity when business continuity is in question. For example - when a team has too many people on vacation at the same time, it will affect the business, a good leave management software should bring this awareness to the managers.