You can login to the app with the same user name and password you are using on the site. Once you are in the app, tap on the "My Houzz" tab and then look for the circular "sync" arrow on the top left (if you are using the iPad app, do this when holding the iPad in landscape orientation).
tap on the sync button to have your ideabooks downloaded to your iPad/iPhone. They will be available there for offline viewing as well.

fantastic. thanks a lot!

For the first time today, I looked on my I phone and saw that my ideabooks were there. Then I synced it, and while playing around, "signed out". When I signed in again, all my ideabooks were gone and there was a message that "you have not created any ideabooks yet!!" How could this happen when I have at least 25 ideabooks. Please advise!

I am syncing again, and hoping all of them will come back. It is taking a really long time to sync. Not sure what is happening.