If you are installing the apk outside of Google Play you need to enable unknown sources first Then, you can install it. The browser should ask you if you want to install after downloading. If not, get a file manager, such as Astro, find the file and click on it.
Run the emulator, if you need the BIOS file the app lets you download it quickly (click Download).
If the app doesn't detect the BIOS it might be because:
1. You didn't place the bios in the right directory
2. The version of the app your are using doesn't work with the version of the BIOS you downloaded
3. The app isn't fully compatible with your phone
Place the Bios in the right directory.
1. The directory might not be exactly the same as the one listed on the website. but you basically have to find the installation folder of the app, and create a folder called "BIOS", then place the BIOS file in that folder.
2. There are various versions of BIOS (European, Japanese, American). If the app doesn't detect the bios, you might want to try to download a version of BIOS from a different source.
3. Try using a different version of the app and see if it solves the issue.