The answer varies somewhat depending on the platform where the Library can access the eBook.
Most of our ebooks are simple PDF files which you can download to your ipad and save to eg, iBooks, the default book app on the ipad.
CSIRO ebooks, and books on EBL, ebrary, and Ebsco Ebooks platforms all use Adobe Digitial editions for digital rights management and are a bit more complicated.
Firstly, set up an Adobe Digitial Editions ID, then install the Bluefire app on your ipad.
All of the CSIRO ebooks may be downloaded, but on the other three platforms, some books may not be due to the permissions granted to those host platforms by the book publisher. Ebsco ebooks display an icon which shows whether a book is downloadable, but on EBL and ebrary you may need to start the process before getting a message saying it isnt available to download, so you have to just try it and see. Also check the number of days for which the book may be downloaded.
I hope this helps - If you have any other problems please include the title of the book you want to download.