10psi would be enough to run a 1-story house with the boiler in the basement. You may have other issues to address other than system pressure.
But to add water, follow the copper plumbing back from the boiler to where the auto-fill valve, which appears to be over your hot water heater. It looks like you may have a gate-valve in series with the auto-filler near the Tee under the floor joists where it branches off to the cold side of the water heater. If it isn't already, open that valve, and if the system pressure is below the preset on the auto-filler you should hear water flowing. If it's already open, there's probably a cam-lever on the auto fill to over-ride the setting and let more water in (the photo isn't clear enough to say for sure exactly which filler valve style that is.)
Be sure not to over-pressurize the system, or you'll have a steaming mess on the floor when the pressure valve on the boiler opens up during it's next burn cycle. I don't see the expansion tank for the system in the picture, but it needs to be properly air-charged for the system pressure too.