If, else and endifs... I dont know

Hi,

I currently have this code:
<?php
if( current_user_can( 'publish_posts' ) ) require_once dirname( __FILE__ ) . '/post-form.php';
?>

I would like tho define in other cases (users not able to post) the file "welcome.php" is shown.

I'n not goot with php so that is why I ask, Ill google it and try and post here my findings, but if anyone can help, I'd really appreciate it.