When searching in databases, it is not enough to type the search terms one after the other, press enter and hope for the best. You should combine search words, and combining is done using AND, OR and NOT. In most databases it doesn't matter whether you capitalize the words or not, but in some it does. Therefore, it is always best to capitalize them. This also helps to distinguish words from search terms better. Some databases have Boolean operators built-in for advanced search, such as the Ebsco databases below.
AND reduces the search and is used when you want all the searched words to appear in the search result. It can also be used to combine words from different subject areas. The more words you combine using AND, the smaller the search result.
AND is often the "default operator" in databases, which can be also left unwritten.
OR expands the search and is used to combine words on the same subject, alternative words, parallel terms, synonyms or words that mean more or less the same thing. The OR operator can also be used to combine words in different languages, different spellings or different ways of expression. When using OR, one of the words must be present in the search result. The more terms in your search are combined with OR, the higher the search result.
NOT limits the search and is used when you want to exclude a word from the search results. When using NOT, you should be careful not to accidentally exclude good and relevant search results.