What I can do with Construction Priority and Buildpower?

https://zero-k.info/mediawiki/index.php?title=Economy_Guide#Priority
https://zero-k.info/mediawiki/index.php?title=Resources_Reserve

You can set the default build priority state of certain unit nanoframes somewhere under default unit states. I recommend setting Metal Extractors to High Priority, because in all cases where I build a metal extractor I want that built first.

When you have low metal income early game(like +13 m/s) the best course of action is to be very granular with your builds, do not build more than 1 unit/structure at a time, because having 1 fully built thing is better than 3 partially built things. You can set your most important construction project to high priority as the most effective way to fast track production instead of microing around your other construction projects.

In the late game where you may have a pack of constructors building front line defenses, and 2 seprate factories producing units, and building up energy economy in the backline, you can apply the same priority system to fast track the projects you think are most important, for instance the frontline stingers, or the factory producing fast moving raider reinforcements. Priority can be thought as a way to pause all other constructions to build something specifically important first.

Large shield generators and cloak/cloak fields and morphable units have a special priority state that determines their non buildpower related economic expenditures.

Resource reserve is useful for when you have incredibly high buildpower instantploping turrets somewhere or as a back up in FFAs.

When you only have 10 metal/sec income, it's better to build one thing at 10m/s and then a second thing at 10m/s than it is to build two things at once at 5m/s each. Both ways take the same amount of time to complete, but the first way gets you thing #1 halfway through the process whereas the second way doesn't deliver thing #1 until both thing #1 and thing #2 are done. Since the sooner you get thing #1 built the sooner it can be put to use, the first way is better than the second way.

In other words, build your stuff in series (one after the other) not in parallel (both at the same time).

In the early game, this means that you don't want to be making units AND making eco at the same time. You want to make units THEN eco, OR you want to make eco THEN units. Usually the latter.

Zero-K gives you an easy way to make this happen. Set your factory priority to low and/or your commander and constructor priority to high. This way, when your com is making eco, your entire income will be directed towards making eco, rather than being split between eco and units. That lets your eco finish sooner - which is good, because the sooner your eco is built, the more eco you'll have, and in the early game you desperately need eco!

When your com is finished making eco and is walking to the next cluster of mexes then he won't be doing any construction, which means that your entire income will be allocated to the next-highest-priority construction, which will be your factory. So while your com is walking, your factory will make units. And when your com starts making eco again, because he's the high-priority constructor, his eco will finish as rapidly as possible, at which point your factory will start making units again as rapidly as possible.

The total time it takes to produce the same amount of eco and units will be the same as if you had left everything at the default priority and therefore split your income evenly between your com and your factory... but the eco will finish earlier which means you'll have more metal.

But that also means your units will finish later. That too has its drawbacks. You need to learn how to balance your needs between getting units early and getting eco early. That's part of learning the game and comes with experience.

But at a first approximation, as advice for a beginner - set your commander's and your constructor's priority to high or set your factory's priority to low. GENERALLY SPEAKING in the early game you're going to be better off letting whatever your com is building get built first, whether that's eco or defense. But be careful that you don't have your com building too much! Build mexes, build just enough energy, maybe build a lotus, then start walking to the next cluster of mexes and let your factory crank out units while he's walking.

Hope that helped! There's a bunch of other fun tricks you can play with buildpower and priority, but from the replay that Godde commented on this is probably where you need to focus for now.