Read the Installation Guide. It covers how to install on your specific device (iPad/iPhone via Safari, Windows via Chrome, etc.) and walks through first-time setup. Your invitation message includes the PDF — review it now if you haven't.
Plan a 7-day testing window. The app gives you a 7-day free trial that unlocks all features. Pick a week when you can actively try the app — ideally with real ORB scenarios you'd normally write by hand.
Connect to internet. Required only for the very first launch so the app can cache itself for offline use. After that, you can use it at sea with no connection.
Understand this is an entry guide, not the official ORB. The app helps you prepare correctly-formatted entries before writing them in the physical, IMO-approved Oil Record Book. The Master, Chief Engineer, and responsible officer remain solely responsible for actual entries.