There are different ways in which you can install an app on BlueStacks 2. They are described below.
1) Search and install: On Home screen,
a) click on the play store icon as shown below:
Type the name of the app you wish to download in the Search box
Click on the "INSTALL" button to install the app.
b) Click on the search icon on home screen
The searched app icon(which is showbox in this case) will be visible and clicking on it will install the app.
2) Drag and drop: You can now drag and drop .apk file of any app on BlueStacks App Player. All you need to to drag .apk file ( present on your system) and drop it on App Player screen. It should start installing the .apk file.
3) Apk button on sidebar: You can now install any .apk file directly from the APK
tab available on the sidebar. Clicking on this button will let you install .apk file saved on your PC.
If you any further questions, please email support at bluestacks dot com.