They just take some getting used to. Each spreadsheet is different, but in general, they allow you to configure your talents and buffs, choose your gear, and it will output your theoretical maximum DPS/HPS etc. Change your gear and gems and enchants around to find upgrades or optimal gear sets.
Everyone should be using these spreadsheets. Nothing more frustrating than having gear in your bank that actually increases your DPS but you didn't know it. Most of us don't have the knowledge or time to be game mechanics wizards, so leave it to the experts. 9 out of 10 times, you'll be fine just blindly following the advice of these spreadsheets.
Remember that character attributes and talents and abilities are all inter-related on a sliding scale. You can't just max one attribute, then another, then another. One piece of gear might be an upgrade now, but that might change when your other gears and stats change. Or, a piece of gear might be a sidegrade now, but become a big upgrade later when your other stats change. These spreadsheets take care of all the complex multi-variable calculations.
