Complete directions are here https://docs.google.com/
Stephen Gasior wrote these for a Virtual Pioneers tour a while back.
Basically, you download a viewer that can access Open Sims. Firestorm has one. Singularity is also a possiblity.
Install and launch the viewer.
Next you click Grid Manager at the bottom of the viewer window.
Click Apply and OK.
You will be directed to a place to register for an account.
Create an account.
Once you get the notice that it is set up, fill in the login name and password at the bottom of the viewer and login.
You will rez, or spawn, in Nova's sim. You may appear to be a cloud, but we can help you get an avatar body once you are there.
Start early! This process may take a few minutes.