So, you have added a plug-in and outgoing e-mail stopped? Then uninstall the plug-in. If your admin web interface too is broken, just delete the plug-in directory in the code tree.
Visvanath Ratnaweera
Αναρτήσεις που έγιναν από τον/την Visvanath Ratnaweera
Do you mean syntax highlighting. For that there is an additional plug-in, the filter Syntax Highligher.
One workaround would be to hide the course. Those with the Teacher role will still see it and can enter.
Step-by-step_Installation_Guide_for_Ubuntu is about installing Moodle which you have successfully done. Now you want to change its URL from http://example.com/moodle to http://example.com/, which is in Moodle jargon a migration. That is where Moodle_migration comes in with that Moodle_migration#Update_links_containing_wwwroot_in_the_database step.