I had to re-read twice also but you need to substract the SP value from the basic hull from your ship points.
So if you rolled 60 shippoints you could take a light cruiser for 55 and add components worth 5 SP. Being a bit funky you'll take the command bridge which adds +1 SP.
They should have removed the plus sign, since it is confusing people. I'm pretty sure any +X SP on the Essential Components are costs, not an increase to what you can spend. (since Essential Components don't normally cost anything). So, a command bridge costs you 1 SP.
I'll also point out that it's a hell of a lot easier to add Components as the game goes on, than to change your hull. So, I would recommend erring on the side of the hull you want, rather than trying to get a lot of Components.