What would be really useful in these kinds of sections would be access to the tables showing the relevant definite articles/noun declensions for the various gender and plural/singular combinations. Once you are actually doing the exercise you can't see them; and Greek is not a popular enough language that such tables are easy to find on the internet.
The combinations αυ ευ are pronounced as /av ev/; and before a voiceless sound such as /t/ the voiced /v/ gets assimilated to a voiceless /f/, thus αυτός is /aftos/.
Since Greek has no sound like our "sh" that needs to be kept separate from "s", the realisation of /s/ can vary a bit more than in English, and may sound a bit like our "sh" at times.
For learners, it's probably best to aim for an English "s" sound as that will definitely be understood.