Hi my name is ***** ***** I will assist you with your query today.
Firstly we need to check your TV can connect to the internet, press the portal \ internet button on the remote (which can be found under the back button half way down on the left hand side).
From here navigate to the internet browser using the arrow keys, then press the OK button to select the application, this will load a web browser, at which point I suggest you navigate to a web page such as google, or bbc to confirm the TV is able to access the internet (you may find it useful to read page 29 of the manual which give you more detail about using the internet browser).
Once you are able to prove the internet is working on the TV, you need to go back the the portal page and then choose the app store which might be labelled as 'Vierra Market', from here this will load an page where you can search for BBC IPlayer and a host of other applications, once you find the application you want you can select the option to install them. Please note some applications can take 5 minutes to install.
Please let me know if you need any else clarified.