First, you need to make sure that you download applications compatible with your Android tablet. I suggest you search the application you want to download on Google Play Store and download it from there. If it doesn't work, check your Internet connection and clear the data and cache of your web browser and Google Play Store service. If it still doesn't work, I suggest you factory reset your tablet. First, you need to turn it off and to press the Power and Volume Up buttons. After that, release the Power button and when the Reset menu appears select Wipe Data/Factory reset option. Follow the on-screen instructions and reboot your device after the process is complete.