You can transfer downloaded eBooks to a compatible eReader using Adobe Digital Editions (ADE) software on your Windows or Mac computer. The instructions are here.
Device notes:
Newer Kobo eReaders (Kobo Forma, Aura ONE, Aura H2O Edition 2, Aura Edition 2, and Clara HD) have OverDrive built into the device, so you can borrow and download eBooks directly from the Kobo catalogue. Learn more about how OverDrive works on Kobo eReaders.