When you are linking from the content or list to some other content, form etc, it is often useful to pass additional value to it. When creating link click on the + on right side to open additional configuration, there is Custom Variables in view, form or list&search link (or Link in the custom link created by http://www.seblod.com/products/559 )
You can use the same format as in templates, e.g. to pass course_id variable and pull its value from art_id field you would write
course_id=$cck->getValue('art_id')You also need to make sure you have added this field - Article id (art_id) in our example - to the list's fields, then you can set Typography to Clear and also its Label to Clear, so that it won't be visible in the list.
When linking from content you could also use
course_id=$uri->getValue('id') this won't work on lists as there is no id variable in url, also each link has different id.