When you are searching for articles and want to get fewer articles that are better focused on your topic, you can use AND to narrow the number of articles you see.
For instance, if you search for Policy AND Globalism, you will only see articles that have both keywords in them. If you add another concept (Policy AND Globalism AND Politics), you will see even fewer results, since all articles now have to have all three keywords.
Some databases require you to capitalize AND when you write it out, so it's a good habit to get into.
When you are searching for articles and want to get more articles that include similar terms that describe your topic, you can use OR to expand the number of articles that you see.
For instance, if you search for Policy AND Globalism, but also wanted to include the concept of Law (similar to policy in some searches), you would write that as follows:
(Policy OR Law) AND Globalism
This will get you all the articles with the keywords Policy AND Globalism, and all the articles with the keywords Law AND Globalism.
Whenever you use OR, always use () parentheses around the two or more concepts that you are saying are similar terms.
The parenthesis are necessary because OR acts like the + sign in a math problem, while AND acts like multiplying.
Policy OR Law AND Globalism will get you all articles with the word Policy, and then a separate pile with Law AND Globalism.
In this case, it's like an algebra equation: you want to multiply (Policy + Law) x Globalism to get Policy x Globalism + Law x Globalism.