> First of all, what are story points? Are they measures of time it takes to complete a story? If yes, then why are they not in terms of time?
I don't think I've ever read the official scrum guide, but ever since I started using scrum (around 2004) the concept of story points was clear: They were "perfect days", i.e. days where you don't have any distractions and nothing goes wrong and everything works first try.
As a fairly experienced developer, I can easily estimate how many of those perfect days will take me to do a task (at least if it's a technology I know). When estimating, the whole team estimates all tasks until there's a consensus (and you are right, ideally, all the stories should require similar effort).
After that, the "perfect day" thing is forgotten, the estimates have no unit and the velocity starts playing it's role.
And here's exactly why I like points: The link between real days and points is lost, it doesn't matter. All that matters is that you completed X points in a specific sprint. Chances are that you'll complete X points in the next sprint. Iterate through a few sprints and you'll have a pretty good idea of what will be finished when.