How to add and install new applications in android TV

You please download "Sideload Launcher" app from the Google Play Store.
Open your Home screen. Find "Apps" by Scrolling to the bottom Then slide and find the "Sideload Launcher" app.
Open the app.
It will show you all the sideloaded apps to your Android TV.
All these apps in this section can be opened through Android TV remote.
Under the sideload folder, there would be an "ES File Explorer". It would be present there, and if not go and download from Play Store.
Open ES File Explorer. Select the "Network" option and then select "Cloud". You will see a bunch of different cloud services including Dropbox, Drive etc.
Now, select whichever cloud storage option you like. Sign-in to your desired service.
Go to Google on your Web or whatever device is connected. Search the app or game you want to download. Keep in mind that the app should be with "apk" After finding the apk file, download it.
Position the downloaded apk game file to your Cloud Storage folder. Now select Cloud Storage through Android TV through ES File Explorer. Now you will be able to see the downloaded apk file there.
Then install that app and there would pop up an error. Go to the Settings option, select Security and checkmark on Unknown Resources. After it is down, press install again. Now the application will download successfully.
Now hop on to the main screen again, select the sideload launcher and see you desired app resting there.

This method you can try.

In your home screen of Android TV select by scrolling down "Apps".

Now select Google Play Store. Search for apps and games of your choice. Some apps will be free and some may have a price. If there is a price then it will direct you to payment which you can make using debit or credit card as per the usual online payment process.

Now download the app and then install it.

If you want to manage the apps then you can go to settings and then various functions like delete etc.