What you should have is a dark and steaming perfectly extracted espresso, topped with a thick layer of crema formed from extremely fine bubbles that is tan to dark red in colour. If you sprinkle some granules of sugar on the crema, it should be buoyed by it for a second or two before sinking. Now, taste it!
Your drink should be rich and aromatic. Or as my father-in-law would say, “it is like an angel pissing on your tongue” (whatever!) If it is sour and watery, the grind may be too coarse and the heated water isn’t staying in the grinds long enough. If bitter and sour, the grind may be too fine and the coffee is being over extracted.
Good luck and most importantly, HAVE FUN with your La Pavoni. Once you “get it”, you’ll wonder how it was possible that you once didn’t.