On a Mac, it’s common practice to install something by dragging a file to the applications folder. From my Windows background, I’ve always known installing things to be different. You click a downloaded executable, wait for the installer to run, choose a directory, and then it tells you it’s installed. Fine. Good. Done. Groovy.
But on Mac it’s different. You download a DMG file (no idea what that stands for, but I literally don’t care. I just want it to work), then double-click it, and fine, that’s all the same. And then, things get a bit different depending on the app, but I’ve noticed that mostly all apps will show you something like this:
Which when you first see it, might be totally baffling. Nowhere tells you what to actually do, and I was confused the first time I had to do this. Luckily I had someone nearby who’s been using a Mac for long enough to tell me to drag the icon on the left onto the one on the right.
Sensible, really, because it’s symbolic of you dragging an individual app into your Applications folder. I like that, but I feel like some instructions are needed, in case this is the very first time you’re installing something! This one by PhoneGap is quite good because at least it’s instructive. 
Not all drag to install processes are the same either, here’s a few other examples:
The difference of design makes me assume that this isn’t a necessity, and is a convention perpetuated by app creators. I’m sure I’ve seen some where you have to drag vertically, and some where you just have to click.
