This stuff is so confusing to me. Is it made the same way as the other two? There must be something different about it.
No, pfizer and moderna use mRNA technology, this uses an adenovirus vector. it's more similar to the astra zenica vaccine in terms of how it works.
The 66% efficacy is based on a single dose and refers to preventing symptoms. It's apparently 85% effective against severe disease and 100% against hospitalisation and death (within the time frame of the trial. There's an ongoing trial to see if a 2nd dose will boost efficacy.
More info here: https://www.clinicaltrialsarena.com/comment/covid-19-vaccine-protection/