Rule number 1: Be patient! Relax! Don’t worry! Give the beer TIME. Don’t fuss over it. When the beer looks like it might be near end of fermentation, take a specific gravity reading. Then wait 3 days. Then measure again. If the gravity reading doesn’t change, it’s ready! If it does, then it’s NOT ready! Don’t be in any hurry. Yeast works at its own pace, and it might not be your preferred pace. Be patient with it, above all else.
Brewing is as easy as you want it to be, and it can be as expensive or difficult as you want it to be. But it can be whatever you want it to be, and you’ll make great beer either way.
Don’t use Liquid Malt Extracts (LME). They are less fermentable and darken the beer, and oxidize fast. Stick with dry extract (DME) and quickly jump to all-grain brewing as soon as you learn the ropes…
Brew In A Bag (BIAB) is the simplest method of all-grain brewing and costs almost nothing to start – you need a big container and a big bag, and that’s about it!
If using tap water (which is just fine), just be sure to get the chlorine out of your water. To do that, add 1/2 crushed Campden tablet per 5 gallons prior to adding any other ingredients. Then you’re all set.
For extract beers, you really should use distilled or RO water. Extract already contains all the minerals in the water that you need, so distilled or RO is best.
Read a book. If you haven’t read up on how to brew, maybe read How To Brew! Or any starter book is fine really.
That’s about it for advice for starting out. All the other little details come as you gain experience. You can easily make great beer on your very first try if you listen to your homebrew shop owner’s advice, and my pointers above, and the folks here on this forum if you have any more questions. You found the right place, that’s for sure! The AHA forum here is the finest on the whole internet, I swear it.