If you go to the Database Search page on the Library's website, you can search for a database either by typing the title into the search bar, or by searching by subject and then browsing the results list. You can then click on either the title or on 'Available online' to open the full record. If the database requires non-Athens authentication, under 'Authentication notes' you will see the link 'username and password available'. Click on the link and this will take you to the Usernames and Passwords for resources not protected by Athens page. Again, you will need to enter your LJMU username and password in order to access this page.
On the Usernames and Passwords page you will find the necessary instructions for accessing that particular database. There may be a special username and password required, or the resource may be IP controlled meaning you can only access it either on campus or by using a University VPN service.