Binary search, and algorithms in general, is a field you must try to get a grasp on no matter what programming languages you work with. Often in a high level programming language you don't need to implement them yourself, but understanding these issues will have profound impact on how well you can learn and exploit a particular programming language. The more algorithms and datastructures you are familiar with, the easier it will be to see good simple solutions to what seems a hard task without such knowledge.

Binary search is the process where you halve the remaining search space for each test. So, lets say you have your dictionary of say 100.000 words in a SORTED array. Now you want to test if the word Trzagrat is in there somewhere. First you look on the position in the middle of your dictionary array. Either you find the word there, or if not, you will know which half of the dictionary must hold the word if it's there at all, because the dictionary is sorted, and the word you're looking up either sorts before or after the word you found at this position. So you contiune...

A better explanation on Wikipedia, binary search