To get the best possible results from your database searches, two things are important.
Use well-chosen search terms.
These are the terms that might be used in publications about your topic.
Use search techniques the database 'understands'.
Your searches should be formulated according to the search rules of the database you're using.
Most databases have similar search rules, so while the databases themselves may look different, once you have mastered one it's much easier to learn how to search others.