Just like with fitness / health / strength, a lot of intelligence is genetic, and there is nothing you can do about that part. But, like with fitness, even more of it is environment/experiences, and we have 100% control of that.
Plus, when you start to understand the underlying reasons for how things work, everything starts to make sense. Once you learn the fundamentals of physics, mechanics, and chemistry, all mechanical things make sense, and you can reverse engineer anything, figure out how it works, and repair it. Once you learn the fundamentals of human psychology and sociology, all human behavior makes sense, and you can avoid conflict and get people on your side, or at least their respect, no matter how different their life outlook may be.
like unlocking the door, dialing a phone, taking a card out of your wallet, or using a spoon or fork.
any time you don't understand, or don't understand 100%, or there is any chance you might be misunderstanding - not just don't understand "what", but also why, ask questions. Ask everyone, about everything; ask so many questions that it starts to get annoying, and then, if there is any remaining ambiguity, ask more questions. Never accept "that's just how its done" as an answer for anything.
It might look like a lot of work at first, but learning is fun. Once you get in the habit, it feels normal quickly. And the effects will make literally every part of life better in every way, for as long as you live.