Well, there are two parts to your learning here.
1. Learn the tools. These are serious professional tools and baffling if you just try to dive in. Worse, if you dive in you will certainly make mistakes, make work hard for yourself, and may need to end up redoing work or doing very poor quality work. A classic example of what happens when diving in: I heard from someone who made office fill-in forms using Photoshop. But a more subtle error is to use InDesign and manually change fonts rather than defining styles.
2. If you purchased a really neat set of carpenter's tools you still wouldn't make a very good cabinet. This is not just about the tools but about graphic design, a mixture of art and craft. If you are lucky, you have an eye for such work and can recognise the bad work around us for what it is - for example, perhaps you can see where there is not enough white space, where there is poor composition of pictures, where the page is unbalanced, the text too tight or too loose, and basically the work doesn't do its job well. Even those with an eye for this can benefit from studying graphic design, but if you don't have that artistic eye, you will need intensive study before you can make brochures to a high standard. Commonly, this is a multi-year full time course.