For very popular e-books you may see a message telling you that the e-book is already in use. Some platforms only allow an e-book to download by one or sometimes three people at a time. In this case you can try accessing the e-book again end of the due date.
In many (but not all) cases you will have to use software called Adobe Digital Editions (ADE) in order to borrow and use e-book offline.
Adobe Digital Editions is free software that allows you to download, view, and manage eBooks on your computer or laptop. The first time you use Adobe Digital Editions to open an eBook you will be asked to download to your computer.
Once you have downloaded Adobe Digital Editions (if needed), you are ready to borrow eBooks. From an eBook record, choose the option to borrow or download the entire book and follow the on-screen directions.
Loan periods for eBooks will vary, like 1, 3 or 30 days. For most eBooks with a loan period, the content will automatically become unavailable after the loan expires.
Hundreds of thousands of e-books are available to you 24/7 from any device which is connected to the internet, so can be used anytime and anywhere. E-books can be accessible on-or off-campus.
Ozu Library e-books collection is multiple collections from different providers. In order to access e-books off-campus, you will be prompted to login with your Ozu e-mail and password.
O’Reilly for Higher Education (Safari Technical and Business Books Online) 
When you click a link from the library website to an electronic resource (e.g. article, e-book or database) you will be prompted for your OZU e-mail and password.
On-campus users will not need to log in.