You need to download a version of the Sibelius software.
There are several versions available, but Sibelius First, the free version, will allow you to view and listen to all the Sibelius files available on our site.
Simply follow the instructions on the Sibelius website to download and install the software. They will probably ask you to create an ‘Avid’ account (Avid own Sibelius), but it is safe to do so.
When you have installed Sibelius, you can double-click on any downloaded Sib(elius) file to view it.
Alternatively, at the time of writing, iphones have a Sibelius app available, which will play Sibelius files.