Searching the term SOCIAL MEDIA gives you results with the words SOCIAL and MEDIA anywhere in the description of the item, but not always as one term together. To search SOCIAL MEDIA as a single term, use quotations to keep the words together: "SOCIAL MEDIA"
Searching the term TEENS gives you results that have the exact word TEENS in the description of the item, but not TEENAGER or TEENAGE or other endings for the root word TEEN. To search a term will all possible endings, use the * symbol (or asterisk) to get more results: TEEN*
Identify subject headings, or words used to uniformly describe or 'tag' the subject of an article or book in many databases. In some databases you can use the THESAURUS function to find subject headings, or try looking for a drop down menu next to the search box.