No. You should be able to use WordPress through the user interface, without ever having to touch PHP.

The only time you would modify your WordPress website with <a title=”Glossary” href=”http://codex.wordpress.org/Glossary#PHP”>PHP</a> would be when integrating some of the <a title=”Plugins” href=”http://codex.wordpress.org/Plugins”>plugins</a>. There are a small number of plugins that still require manual edits to your files. In most cases, clear instructions are usually given within a text file with the <a title=”Plugins” href=”http://codex.wordpress.org/Plugins”>plugin</a>.

Other than that, you would not be changing any of the <a title=”Glossary” href=”http://codex.wordpress.org/Glossary#PHP”>PHP</a> files.