Search statements are the Boolean Logic equations you put in the database search engines. Like math they can be extremely basic (Dogs AND Cats = 1 + 1) or more complex. The more complex methods are to save you time doing multiple searches, and if done properly can help you refine your results so you get exactly the ones that will answer your research question.
wildfires AND ("climate change" OR "global warming")
Common advanced tactics include: Truncation, Synonyms, and Nesting.
Truncation is used to search for variations of a word that the database might not automatically find because they are irregular words.
Truncation is all about going back to the root or stem of the word and searching for any words spelled differently after that root. It is also known as wildcard searching, because you are searching for variations of the words. Commonly an asterisk (*) is used after the root, but some databases use a question mark (?) or money sign ($).
If your question was about teenage obesity, then you could search for all the variations of teen by using that as the root.
If you searched for teen* you would get: teen, teens, teenager, teenaged.
If you searched for variations of health using heal* you would get: heal, heals, healed, healer, healing, health, healthy, etc.
Truncation is good for variation of words that are more complicated than just adding an s to make it plural. So if the root of your word is common, you should probably not truncate it.
As explained with OR, synonyms are best used when keywords are commonly used interchangeably and searching only one is limiting your potential results.
A topic such as "wilderness therapy" can also be called "survival therapy." Children are also commonly called kids. "International adoption" is also known as "interracial adoption" or "cross-cultural adoption."
It could also be something that has multiple spellings, such as Ketchup or Catsup.
Searching for synonym keywords ensures that you don't miss out on good results just because you were only using one of the preferred terms.
Nesting is how you put the different tactics together, and is a lot like a math equation, in that it helps the databases group synonyms and operators so it knows how to search them. It also helps longer, more complicated search statements look more manageable.
Synonyms (OR) should be nested in parentheses.
(Ketchup OR Catsup)
A nested search statement could look like:
(Child* OR Kids) AND obesity
or
("wilderness therapy" OR "survival therapy") AND teen*
What each of these search statements is doing is combining the searches for the synonyms into one search statement:
child* and obesity 
+
kids and obesity
= (Child* OR Kids) AND obesity
or
"wilderness therapy" and teen*
+
"survival therapy" and teen*
= ("wilderness therapy" OR "survival therapy") AND teen*
You can also further refine your results by using the limiters in your database. In Academic Search Ultimate, all the limiters are located on the left hand toolbar of your results page, called Refine Results. With these tools you can limit your results by:
Using these limiters to refine your results will help you get fewer results that will be better for your research as they will be readily available, peer reviewed, and/or more current then the eliminated results.