Hi and Welcome on the forum,
There's a couple of different approach you can use. Depending of the accuracy you may choose one of the following

1) A R2R network. So basically a couple of resistor attached to a single or multiple port then you mix them like a traditional OPAMP summing amplifier Like This
2) PWM signal, then you filter with a low-pass filter. Usually a simple capacitor and op-amp buffer
3) Dedicated DAC chip. And still there, you have different flavor, 8,10,12 bits

Choice is yours.