There's a regulator at the gas meter. Both that and the meter must be capable of the volume of gas you require. Usually, the input to that is of high enough pressure that you would be unlikely to overload the supply. THen, the gas moving through pipes and fittings in the house will experience friction, which will limit how much volume can flow through. The regulator will keep the inlet pressure constant as long as you're not asking for more than it can provide, but friction to the devices through the piping will determine if the pressure drop is out of spec for the volume of gas the devices are designed for. Longer pipe, smaller diameter, more fittings, all affect how much can flow through the pipes. It should be designed for worst case when all devices are calling for maximum at the same time. That takes some calculations.
Ever tried to drink a milkshake with a small straw? Really tough. Your gas appliances don't 'pull' the gas through, but the pressure is quite small...the opening must be large enough, or it won't work well, if at all.