Football coaching is a huge topic and also one where everyone has their own opinions. It is therefore important to say straight away that we aren't expecting our coaches to have an in-depth knowledge of every facet of the game. It is important however to have a good basic knowledge of what we are doing.
Imagine a situation where you were required to coach someone to become a figure-skater. Unless we had the basic building blocks of knowledge to teach them how to skate initially then it would be impossible to get them to a level where they could dance on ice. The same is true of football - we need the basic building blocks of knowledge in place before we can hope to progress to anything more complex. This can be brought right back to even the most simple of concepts like kicking a ball - do we know which part of the foot to strike the ball with for shooting? for passing? Do we know the correct position for our standing foot? etc. All of these little things are important to know and without the basics in place we will struggle.
It is important, therefore, that we try to educate ourselves as much as possible. This can be through reading, watching training videos, observing other coaches work, going on a coaching course or many other alternatives. Online courses like this one are another resource open to you. This particular course looks at what it takes to become a coach but there are other courses available on this site which look at specific training techniques.