The drag and drop thing is because it’s an app file. “Installation” is just putting the file in your application folder, or wherever you want it. Apps are (usually) just files, unlike on windows, so you don’t need to go through a complicated installation process, just put them where you want them (usually the applications folder).
The window snapping thing is annoying (but it’s not apple’s fault, Microsoft has a patent on it lol). There’s a bunch of free apps that add window snapping though 🤷♀️