You might wish to first test auditing a Windows computer. There are a couple of ways to do this, but perhaps the easiest is to browse to the Open-AudIT logon page using Internet Explorer on the system you wish to audit and click the link "Audit My PC".
When you do that, you will see Windows prompts - click "Open" and then "Run".
The dialogs will disappear and nothing will appear to happen (we have this on the list of items to improve). If you open the task manager you should see a "wscript.exe" task running. This indicates the audit is running against this PC. When this process finishes you should see a new Group (or two) on the homepage after you log in to Open-AudIT. Congratulations - you have just audited your first computer!
Other ways to audit individual Windows computers are detailed in How to audit a single Windows computer.
From here you can start creating Locations and Organisations, auditing your fleet via active directory, discovering your subnets, running reports and more.