The light blue circle contains and aircrafts Primary return with and SSR return overlaid, not necessarily identified; the to 4 digits of the label are the assisgned SSR code, below that is the Mode C readout and an arrow to indicate whether it's climbing or descending.
The green circle depicts a Primary return for an aircraft.
Yes the white lines indicate the extended centrelines, the background shading indicates different types of airsapce.
And the small, numerous orange dots are Primary returns which are clutter; terrain, weather, birds etc....
However as a previous poster explained; mountains and such are usually filtered out by use of MTI.