Hostess
Hostess is a free utility for maintaining your Hosts file. The documentation included with Hostess can give you a general overview of how the Hosts file works as well.
Unlike many Hosts utilities, Hostess is geared towards ad-blocking rather than IP address resolution. Hostess stores your host entries in a database that is indexed to eliminate duplicates and make searching fast and easy. It also allows you to group these hosts for efficiency and ease of maintenance.
Installing the program is also easy: just create a directory, unzip hostess.zip into it and create a shortcut to hostess.exe. No registry changes are made, and any program settings are stored in an INI file in the program directory.