[General Questions and Answers] 5h1v4u:
You need a rooted device. There are few applications that do not need root, but I do not know about them.

And I am not responsible for any damage caused to your device.

Not available for country

I was told there are so many ways but none of them are working now due to some restrictions by Google and I am able to download the applications that are not meant to my country (India) and that are not meant to my device.

In order to do that, we need a VPN application which makes the servers think that you are browsing from the allowed country. But that's not it. You should also have a Google account that's created in that country. So if you want to download an application that is only available for USA, you should have the Gmail account created in USA (in our case, USA servers).

There are so many VPN applications availabe on the store as well as from unknown sources to download.

I have tried VPN One Click, Hideman VPN, and DroidVPN personally and liked all of them. I was not really sure that these are well trusted, I will leave about them to you so you better check the review before you download them.

Basically, we are here trying to bypass your service providers IP address and make the online services (websites or play store) look like you are connected from a different country. So download your choice of VPN application and install it. In our example, let us think we are downloading an application that is meant for USA. Once the VPN is installed, set it to access through USA servers.

Now open a web browser and check yourself that you are directed to the USA based websites when search for something. Once that's done, create a dummy Gmail account. Once created, open Play Store, tap on settings > Accounts > Add Account. Now add the dummy account to your Android device. Make sure the Play Store shows both the accounts. It doesn't matter which was set to default, you can always change it. After you have added it, the apps will be downloaded/synced. You don't need to sync all your device data to this dummy account.

Now we have to delete all the data of the Play Store. Go to Settings of your device > Apps/Applications. Search for Play Store and tap on "Clear Cache" and "Clear Data" then Force Stop the app.

Now Re-Open the Play Store and you should be asked to accept the Terms of Services (make sure the VPN is still running and account of Play Store should be set to the dummy Gmail account). You should be placed in the USA based Play Store. Now you can search for the app and download it.

Not available for device

This will be helpful if you want to download an app that's not available for your device but you want to try it.

There are again so many apps that makes masks Play Store service. Out of which I have used is called one that's called Market Helper.

Download and install this app to your device. Open it and choose the type of device you want to make your device look like. In this case, we again are trying to download a Galaxy S3 supported app on non supported device. So select the type of your device as Phone and the phone as Samsung Galaxy S3. Set the Operator to USA and AT&T or anything else. Once all set, tap on Activate. Now go to Play Store and search for the application that's not available for your device.

Note : If you are trying to download an application that's not available in your country and also for your device, you need to setup both of the above instructions.

If you are having difficulty after trying everything, unlink your Credit Card details from your Google Account. You will have to log into Google Wallet to remove it.