APK stands for Android Package Kit — it is the installable file format for apps built on the Android operating system. You can download an APK file directly from a site or official channel outside the Google Play Store and install it on your phone; this is commonly called "sideloading".
The 67 bd Android app is available as an APK, which you get through the official channel. A separate version is also available for iOS users. Once installed, you can access the slots, live casino, and sports betting sections of 67 bd Casino directly from your phone's home screen — no need to open a browser.
You do not need any third-party site or unknown link to get the app. Only get the APK through the official channel — it is safe and verified.