You can use pearl-growing if you are still in the orientation phase and do not know exactly with which (key) words you can search. Do a search and see if there are better search terms in your search results. Then search further with the newly found terms.
Example
You start with a search in START and see if the results contain good, useful terms or keywords. In the picture below you see all kinds of terms under 'subjects' with which you can continue your search. All you have to do is click on them.