Spell Check
Be sure you have spelled your keyword correctly. If the spelling is correct and your keyword still does not return any results, try a similar keyword or a different form of the keyword (e.g. plural or possessive). Also, typing a portion of a word will find all variations of words based on that portion (example: "install" instead of "installation")

Using the word "AND"
To find content which explains installation as well as maintenance, try typing: "install AND maintenance"

Using the word "OR"
To find content which contains may explain either installation, or maintenance, or both, try typing: "isntall OR maintenance"

Using the word "NOT"
To find content which explains installation, but does not contain the word "maintenance", try typing in the keywords: "install NOT maintenance"

Final tip
The search engine is not case sensitive, so whether you type "install", "Install", or "INSTALL", you will receive the same results.