Digital means ones or zeros as in binary or it can mean displaying digits, which I assume you mean.
My bike has a digital fuel indicator as in binary. It emits a buzzing tone if there is fuel, goes silent if there is no fuel.
I assume your digital display has one wire or two or three wires that need to go to the tank?
Yes, you need a fuel level sensor of some sort. Most put out an analog signal, typically 0-5v or varying resistance.
Low voltage and very low current are used to protect from sparks or heating in case of a short.
Most are one or 2 wires, have a rheostat with varying resistance, typically 0-180ohms
3 wires are a potentiometer that has 0v, volt supply and signal wires. These are rare and gauge specific.
Most cheap senders are floats but there are solid state pole type marine senders (sensors) that typically run about $100.
