<?php
// first we name the class (i have named it text_stuff)
class text_stuff {
    // this function will make whatever text you choose bold
    function make_text_bold( $text ) {
        $output = "<b>" . $text . "</b>";
        return $output;
    }
    // this function will make whatever text you choose italic
    function make_text_italic( $text ) {
        $output = "<i>" . $text . "</i>";
        return $output;
    }
    // this function will make whatever text you choose underlined
    function make_text_underline( $text ) {
        $output = "<u>" . $text . "</u>";
        return $output;
    }
}
// this loads the class
$txt = new text_stuff;
// here is how you use it
echo $txt->make_text_bold( "This text will be bold" );
echo $txt->make_text_italic( "This text will be italic" );
echo $txt->make_text_underline( "This text will be underlined" );
// you can even use multiple ones by putting it inside each other
echo $txt->make_text_bold( $txt->make_text_italic( "This text will be bold and italic" ) );
// and even more 
echo $txt->make_text_bold( $txt->make_text_italic( $txt->make_text_underline( "This text will be bold and italic and underlined" ) ) );
?>