I am flying Ethiopian business class to Cape Town in a few months so I thought I'd take the chance to start earning points on Star Alliance. This will be my first flight for ages with them. Can you still redeem from a flight 2.5 years ago?
I was having a quick skim of the Star Alliance rewards page and I'm a bit confused:

"You can join multiple member airline programmes if you wish, but they are each managed separately so you cannot transfer miles or points between accounts or combine them. Using a single programme whenever you fly means you can earn privileges and reach Star Alliance Silver or Gold status faster. "
So do I just sign up to Star Alliance or do I go with a specific airline? the former how do I ensure that my points go through to star alliance?

Thanks