The simplest way of using Patterns is just calling the Patterns::out method to send a pattern to the browser:
This will read the file
/patterns/pattern.html, parse and output it to the client as the
payloadof an ResponseTextHtml response.
You can change the directory where your patterns are stored by setting the
directorykey of the Patterns module configuration file.
But this is just the most common way of using a pattern. You might need to simply get the results of a parsed pattern in a variable. For doing so, instead of using the Patterns::out method, you use Patterns::parse like this:
$parsedContents = $e->Patterns->parse("helloworld.html");
Since patterns are parsed as PHP code, you're strongly advised against parsing files that are uploaded by the user or coming from untrusted sources.