What is the PEAR library?
PEAR (PHP Extension and Application Repository) is an object-oriented PHP library with separate classes for a variety of functions including mail, database interactivity, date and time, encryption, images, HTTP, HTML and much more. For example, the HTML_Form class is used to assist in the automatic creation of HTML forms. Even more useful classes include the File class, used for reading from and writing to files on the file system from which the PHP application is being executed from. An even more interesting class in the library is the File_SearchReplace class, which automates find and replace operations for files where you may want to find certain strings and replace them in a specific file.
The PEAR library is incredibly robust and useful. You do not need to use the PEAR library in order to connect to and interact with databases, as there are built-in functions and extensions in the PHP language itself, including the object-oriented PHP Data Objects Extension (which is also very easy to use).
Read more about PHP Data Objects: Accessing and Using Databases using PHP Data Objects