There are 3 kinds of locks in SQL Server
i.) Shared locks - they are used for operations which do not allow any change or update of data. For e.g. SELECT.
ii.) Update locks - they are used when SQL Server wants to modify a page. The update page lock is then promoted to an exclusive page lock before actually making the changes.
iii.) Exclusive locks - they are used for the data modification operations. For e.g. UPDATE, INSERT, or DELETE.