load(): Load a piece of html into a container DOM.
$.getJSON(): Load a JSON with GET method.
$.getScript(): Load a JavaScript.
$.get(): Use this if you want to make a GET call and play extensively with the response.
$.post(): Use this if you want to make a POST call and don't want to load the response to some container DOM.
$.ajax(): Use this if you need to do something when XHR fails, or you need to specify ajax options (e.g. cache: true) on the fly.
This document outlines the steps that are necessary in order to make your AJAX application crawlable. Once you have fully understood each of these steps, it should not take you very long to actually make your application crawlable! However, you do need to understand each of the steps involved, so we recommend reading this guide in its entirety.