ProQuest is actually not a database, it's a company that hosts many databases. Access ProQuest via the A-Z Database list.
The front page of ProQuest is the Basic Search. To choose the database(s) you want to search, click on the Databases tab. This will lead you to the Select Databases page, where all databases on the ProQuest platform to which Tilburg University has access are listed. You can select individual databases here.
You can also search any one of the ProQuest databases individually by selecting them from the A-Z Database list.