You should add jQuery as a dependencies for the scripts that depends on jQuery.
So instead of
array( 'jquery' )
Also you don’t need the
is_admin() stuff. The
wp_enqueue_script action only runs on the front end.
I’d recommend you to learn how the native wp functions work and don’t rely on tutorials, when a client requests explanations you can’t just say “But wait!!! I got this from a tutorial so it must be correct!”. With this attitudine you’ll probably fail in the long-run. It’s ok to rely on tutorials to learn new stuff, but understand them, not copy paste, clients aren’t going to learn you how it works.
Just my 2c