If you want to do this easily from within Android Studio then on the left side, right above your file directory you will see a dropdown with options on how to view your files like:
Project, Android, and Packages, plus a list of Scopes.
If you are on Android it makes it hard to see when you add new folders or assets to your project - BUT if you change the dropdown to PROJECT then the file directory will match the file system on your computer, then go to:
app > src > main > res
From here you can find the conventional Eclipse type files like drawable/drawable-hdpi/drawable-mdpi and so on where you can easily drag and drop files into or import into and instantly see them. As soon as you see your files here they will be available when going to assign image src's and so on.
Good luck Android Warriors in a strange new world!