Your unique school URL will have been given to you by your school/teacher. The URL address might be provided as a printout, in a letter, emailed to you, or the school may have put it on the school website. It will always look like this: https://onwordshark.com/? with the end part unique to your school.
When you type or copy the URL into your search engine, you should use the address bar which will give you the exact Wordshark Online web page, as per example below. The address bar is always located high up, as opposed to the ‘Search’ box (usually further below).