Watch the video shown above, then go to the Library's A-Z Databases list (https://libguides.ucmerced.edu/az.php). There are a number of databases listed on the right under "Popular databases." Take a look at two databases listed there: Academic Search Complete, an EBSCO database, and PsycINFO, a ProQuest database. Try a few searches in each database for practice.
As mentioned above, even though the video focuses on PsycINFO, the technique can be used across all databases that have a similar thesaurus, sometimes also called an "Index" or "Subject Terms" (depending on the vendor/provider).