Here is a list of all topics with brief descriptions:

Building & signing packages:
Build API.	API for building packages
Signature Tags API.	List of signature tags
Signature API.	How to add or remove a signature from a package header
Data types:
RPM data types.	The abstract RPM data types
String Manipulation API.	String Manipulation API
String Pool API.	How to store strings in pools
RPM version API.	Rpm version comparison API
(un)Installing packages:
Dependency Set API.	How to compare dependencies
Callback signature & types.	The signature of function to register as callback and the cases where it can be called
Transaction Set API.	How to create, run & destroy a package transaction
Transaction Element API.	How to retrieve information from a transaction element
Problem Set API.	Problem Set API
Problem Element API.	Problem Element API
Verify API.	How to verify a package
File Info Set API.	File Info Set API
File Info Set Iterator API.	File Info Set Iterator API
File archive (aka payload) API.	File archive (aka payload) API
File Classification API.	Structures and methods for build-time file classification
RPM keyring API.	RPM keyring API
Macro API.	Macro API
Logging API.	RPM Logging facilities
RPM crypto API.	RPM cryptography related APIs and constants
OpenPGP API.	OpenPGP constants and structures from RFC-2440
RPM plugins API	Structures and methods for developint RPM plugins
Querying package headers:
Header API.	How to manipulate package headers (which carries all information about a package)
RPM Tag API.	Manipulating RPM tags (accessing values, types, ...)
RPM Tag Data Container API.	How to retrieve data from package headers
I/O
Database API.	Opening & accessing the RPM database
RPM IO API.	The RPM IO API (Fd_t is RPM equivalent to libc's FILE)
File and Path Manipulation API.	File and path manipulation helper functions
URL Manipulation API.	A couple utils for URL Manipulation
Argument Manipulation API.	Argument Manipulation API
Command Line API.	Parsing RPM command line arguments
Signal Queue API.	Signal Queue API
Statistics API.	Statistics API
RPMRC.	Reading config files and getting some important configuration values
Miscellaneous utility APIs	Miscellaneous utility APIs