By default, the search uses an explicit AND operator. When searching for multiple words, i.e. safe cracker, all words must be present in the content.
You can also use an OR operator, which is the pipe (|) character. Searching for safe | cracker searches for content containing either safe or containing cracker.
You can exlude words by preceding them with a minus (-) character. Searching for safe -cracker will match all content containing safe but not containing cracker.
You can do phrase searches by using double quote characters ("). Searching for "safe cracker" (note the qoutes) will only match content containing the words as a phrase.
You can use a proximity operator with a tilde (~) character. This will match words in close proximity to each other. Searching for "earthshaker whirlwind"~5 matches em> (note the qoutes) will only match content containing the words earthshaker and whirlwind with less than 5 words between them.