To re-iterate what everyone else said above, you cannot directly use .psd files in Android development.
You can however take these Mockups and slice them into smaller components (or smaller image files in .png for example) and use the images as backgrounds in your app.
For example, in my calculator app (https://play.google.com/store/apps/details?id=tonyebrown.calc8&hl=en_CA), I designed the UI entirely in Photoshop as a mockup, then sliced each element (screen, buttons, background, etc.), exported them in Photoshop, then imported them into Android Studio as resources that I used to build the UI.
The main benefit of doing this is more design freedom.
The downside, you have to work on making sure it works on multiple screen sizes.
Cheers!