The whole activation process was rather complicated. Or at least, there's lots of steps.
For me I did it as follows:
1) Ordered Presto card
2) Waited and waited. Thought maybe they declined my card or something.
3) Presto card magically pops up in the mail. Maybe because of the postal strike it took so long
4) Punched in my card number on the website. I don't remember exactly what happened, but I knew I couldn't do much at that point. It just told me I had to activate it by tapping it at a machine
5) Drove to a GO station, used the balance checker, couldn't really read what it said, tapped it a few times until I was sure I was reading it correctly, and it said I had my $10 balance (that's how much I loaded, yes I'm a cheap bastard lol)
6) Went home, went online, and finally was able to login properly. I thought I might be able to set a default trip online, but no, you can't do much online
Not sure if that helps. I'm sure someone else can explain the process better.