Note in the following image that a siamese cable has a BNC connector at both ends and a pair of wires that to power the camera, at one end there's a power connector (also known as P4 connector in some countries) and on the other side the red and black wires are connected to a power source.
If a cable without parallel power cord is used (such as the black cable shown in the picture), it will be necessary to use a separate power cable, which may make the project a bit more expensive, but in some cases this solution is more professional, especially when the cameras are installed far from the DVR and the parallel cable is not good enough to carry the power.
