One way to start searching is to identify the key concepts within the topic or question, and develop synonyms for these concepts. This gives keywords to start searching with, and you can add more synonyms as you examine individual articles. If I was conducting a literature review on "Mobile apps used to improve medication compliance in type 2 diabetics," my table might look like this to start. I'll fill in other terms as I search.
|Mobile apps||Medication Compliance||Type 2 diabetes|
In a keyword search, the database retrieves articles that use the search word. "iPhone" brings up articles about iPhones only, not about mobile phones, Windows phones, Samsung, or Androids. Usually you care about a concept (using mobile phones), not the exact word used to describe it (such as the brand name). You can brainstorm all related keywords and include them in your search, or, some databases use subject headings to help you conduct a search for a concept.
Databases with subject headings identify one term (a subject heading) to describe a concept. Then every article about that concept is tagged with this subject heading. If you search using a subject heading, you will retrieve every article about the concept. Search PubMed for "Mobile Phone"[MeSH] and you will retrieve articles about all types and brands of cell phones.
Using subject headings is not required for every search, but can be helpful when you need to do a more thorough search, if your concept has many possible synonyms, or if you are not finding enough information using a keyword search. Use the tutorials below to learn to use subject headings in some commonly-used health sciences databases, or ask a librarian.