Segment screen question

isn't the blue pointer you at the present time and the white dot your PR time

Or are you talking about the one below on the green slope?? if so, no idea!

The blue dot on the elevation profile is your position on the segment. The white dot below the elevation profile line is the position of the VP. In this case your PR. You are currently 31 seconds behind your PR time.

but if this green slope is representing all segment how could this blue dot be my current position if segment has just begun (look at progress bar)?

The blue dot is correct. You are not viewing the whole segment there. If you look very closely there is a black bar on the progress bar just at the tip of the white arrow. What you are viewing is just that section of profile, from the start to the black bar. It is a zoomed in view. As you ride it you will see 2 black bars on the progress bar that show what section of the total segment is being viewed.