Use the adjective much to mean "a lot" or "a large amount." If you don't get much sleep the night before a big test, you don't get a lot. If you get too much sleep, you may sleep through your alarm and miss the test.
Much is used as an adjective or adverb, but it always means a large quantity, extent, or degree. When something hurts very much, it's very painful, and when your friend says your gift is very much appreciated, she's emphasizing how happy it made her. The Middle English version of this word was muchel, "large," from the Old English micel, "great in amount or extent."