Programmes that support Audio description have the symbol [AD]. You can check for the icon on GUIDE or by pressing the 'i' icon on the remote control on a selected programme.
To enable the Audio description :
Go to Settings -> Personalization -> Accessibility -> Select the audio description option by pressing OK on your remote control.
You can also enable 'audio description' by playing the programme and selecting the setting icon on the panel displayed at the bottom of the screen. Use the right key on the remote to select 'Audio description'