Build orders are simply a guide to which buildings need to be built and in what order so you can speed build tanks in a short time. These build orders are from some Top Global Dominance players. Just keep in mine this is only a general guideline to follow. As with anything, the more you play the more you'll learn what works best. Generally speaking, you should build an ore truck after you build five tanks in order to keep the money flowing.
Some players opt to build the ore truck before building tanks.
And never let your power go too low. If you do it will slow up your build times. Also, keep in mind you'll need to adjust your build order depending on the type of map your playing on. On maps with less gems you'd have to build more ore refineries early on to keep a steady cash flow. Make ten infantry and two engineers fast, then sell your barracks so you don't run low on power before you build your second power.