Double-click on the !BBCIndent program icon to load its icon onto the icon bar. Drag a BBC Basic file to the bar icon to enter its file name into the main 'SetUp' panel slot. Alternatively clicking on the bar icon brings up the main 'SetUp' panel and the file can be dragged to this panel, or the file name can be typed manually into the slot at the top of this panel.
Select options from the 'SetUp' panel, and then click on the 'Run' icon. After a while a BBC Basic File is offered for saving in the same directory as the original file, but with the leaf name prefixed by a capital 'I'. This is the resulting indented file.