Every players start with a pre-build base :
Defenses like [Tesla Coil]...
1 [Chronosphere] and 1 [Iron Curtain]
Some Power plants
2 MCV (as unit, so same faction as you pick before game start...)
4 [baracks]
1 [dog's house]
And some units so you can scout a bit in your own base
Around 578K ore
Some walls and Defences (from CPU not from any other players...) to prevent early rushes
(mainly [Turrets] [Bunkers] and Navals units)
ALSO
Be careful, the water is not as safe as it seems...