ADHD is a huge topic and there are many resources to choose from if one wants to learn more.
A psychiatrist recently shared this resource with me and I found it very useful—it deals with both adults and children.
I trust you will also find this resource helpful.
By the way, I am often asked if ADHD is over-diagnosed and over-treated. I think it is. But at the same time let’s not use that argument to miss the legitimate ADHD patients who do benefit from proper intervention (Which is a combination of medication and psychology.)