A disabled account prevents a user from logging into the system. A disabled account must be enabled by another user before it can be used again to access the system.
From Setup > Users, search to find the user(s) you want to disable or enable or click the down arrow next to the Search button to reveal and select the option to show all results. Select the user(s) you want to edit. Use the account status filter to search for disabled users.
Open the task list and select Create / Edit Users and click Start.
Select a user from the list at the left of the screen.
Toggle the account status between Enabled and Disabled, as appropriate.