Think of it like the sounds of German ach or Scottish loch but a bit lighter. Wikipedia also has a page dedicated to the sound, with audio examples.
They do describe verbs, but that's not the full extent of it. Basically, broadly speaking, adjectives describe nouns and adverbs describe anything else. :)
If it's an adjective describing maskin, you should be able to simply remove the other adjective and get a completely grammatical sentence. But "It's a very machine" doesn't make any sense, since "very" affects "expensive".