mysql> help contents
You asked for help about help category: "Contents"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Account Management
   Administration
   Compound Statements
   Contents
   Data Definition
   Data Manipulation
   Data Types
   Functions
   Geographic Features
   Help Metadata
   Language Structure
   Plugins
   Procedures
   Storage Engines
   Table Maintenance
   Transactions
   User-Defined Functions
   Utility

mysql> help Functions
You asked for help about help category: "Functions"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Bit Functions
   Comparison Operators
   Control Flow Functions
   Date and Time Functions
   Encryption Functions
   GROUP BY Functions and Modifiers
   Information Functions
   Locking Functions
   Logical Operators
   Miscellaneous Functions
   Numeric Functions
   Spatial Functions
   String Functions