Subject searching is more precise than keyword searching. Subjects are like tags on social media -- they have been added by a person and describe what topic(s) the resource is about. Each individual topic has only one subject per database but could often be described by several different keywords.
Always check the works cited/references of the helpful sources you have found already to see if they lead you to other a little bit older helpful sources. You can also search your best article's title in Google Scholar where you can see what more recent sources have cited your source.
Remember: always save the permalink to your search results not the URL! Permalinks are called a variety of things permanent link/stable URL/etc but are almost always accompanied by a link symbol. Save this link instead of the URL because URLs expire in many library databases.
use AND when you want search results to meet multiple criteria (ex: be about puppies AND kittens)
use OR when you want search results to meet one of several criteria (ex: be about puppies OR kittens (also includes results about both))
use NOT to filter out search results you know are irrelevant (ex: drive NOT cars)
quotation marks keep phrases together (ex: "piano teacher")
asterisks are helpful for searching for all results that have the same root (ex: motivat* will bring up search results for motivation, motivate, and more)