Conglomeration is a fancy word for a bunch of stuff brought together. People, companies, ideas, and other things can group together in conglomerations.
If you ever want something and you're asked why, you could show off your vocabulary and say, "I have a conglomeration of reasons!" That means you have a bunch of reasons that may or may not be connected. A huge mob of people could be described as a conglomeration — which sounds nicer than "mob." The "with" should be a reminder that this is a word that brings things or people together. In the dictionary, you'll find a conglomeration of words — like "conversation" and "concert" — that use con- to suggest a bringing together.