You can choose the files a few different ways.  To choose the files before you add a torrent, when you tap on a torrent link or magnet link in your web browser and choose to download it with our app, a popup will prompt you to select your files from within the torrent & choose a location before downloading.  Tap Files To Download, then uncheck the files you don’t want to download.  Then tap OK, then tap Add.  

Alternatively, you can choose the files after the torrent has already started downloading.  To do this, tap on the torrent, this will send you to the Files page.  Next, tap on the three dots menu next to the file you wish to exclude and tap on Exclude.