Use a keyword search to search all parts of a source for the words you enter in the search box. This type of searching uses "natural language" and is one you're probably already familiar with--you simply enter words or phrases into a search box that you think are relevant to your topic.
When doing a keyword search it's a good idea to try a number of different search terms and phrases. Don't be discouraged if your initial keyword search brings back too many, too few, or irrelevant results--you'll want to try multiple keywords, synonyms for your keywords, different combinations of keywords, etc. to bring back the best results.
For example, if you are looking for information about the dangers of texting and driving you may start out with keywords like: texting, driving, distracted driving, danger, cellphones, etc.
But you'll also want to try using synonyms for keywords (e.g. cellphones = mobile phones, smartphones, iPhone, etc.) and combining keywords (e.g. texting and driving, distracted driving and danger, etc.) to get better, more thorough results.