Consider the following research question:
How do transposable elements interact with telomeres in Drosophila melanogaster?
Let's break it down into concepts, find synonyms for this concepts, and create a search strategy.
Start with two of our concepts: drosophila AND telomere. We want articles that are about both concepts at the same time - this is why we use AND.
Using telomer* we can find additional results, such as articles that use these terms: telomeres, telomeric, telomerase, etc.
Let's add in our third concept: transposable element.
Looking through the search results for the previous search, we see some articles using the keyword retroelement - let's add that in using OR. This belongs with the transposable element concept, just a more specific type of transposable element. To grow a concept, remember that "OR is MORE".
Doing some research online, we see that the terms retrotranspoon and transposon might also be relevant to the search. We can add those in using OR as well.