The search box looks for the words you type inside the titles and the text of every page on the site.
Two things are worth knowing, so that search does not surprise you.
Search looks in every script, whichever one you are reading in. A page is a result if the words you typed are anywhere in it, in any of the scripts it exists in. So you can search in Kannada while reading in Romi and still find things. The result is then shown to you in the script you read in, which is why a result sometimes does not have your words visibly highlighted on it: they are in another version of the same page.
Search matches words as they are written. It does not yet understand that two spellings of the same word belong together, and it does not find a word by its root. Spelling in this archive is not consistent - it was written over many years by many people - so if you do not find what you expect, try a shorter word, or a different spelling, or browse the publication instead. We know this is a limitation and better search is planned.