When an article is published it will included references to resources that the author(s) of the article have used to support their argument. In the language of articles, the term reference / citation are often used interchangeably and are a way of referring to the details of the paper (usually an article) that those authors have used.
References will generally be older than the article they're mentioned in or, at the very least, the same age. So an article published in 2010 may have references for articles from 2010 and older.
Citation searching is a way of looking to see which more recent or up to date articles have used a particular paper in their own research. Their research will hopefully be on the same or a related topic and so may lead you to more information. This can be particularly useful if you're not finding many results for your topic.
As a starting point you would identify an article that looks particularly useful, or that supports your argument very well but is perhaps a little older than you would like, and then search for that article title in Google Scholar. When you get the result on screen it will hopefully have been cited by other, more recent papers and you can see a list of them.
When you search individual databases they will often (but not always) say how many times a specific article has been cited by other articles in that database. So it won't be a complete list as it's limited to that database. For that reason, when you look for the same article title in Scholar your results - the number of citations of that paper - will often be higher. Not necessarily by a large amount but they will most likely have gone up a bit.