The first layer in OSI model is called Physical layer. It is working directly with the hardware, sending and receiving signals through the Network Interface Card (NIC).
While changing voltage for the copper wires it also can use light pulses for the fiber-optic cable. If the NIC has wireless receiver/transmitter it can receive/send signals as the electromagnetic waves.
After signals are detected they are passed forward to the Data Link layer. Also, it is necessary to note that hubs and repeaters in the network are operating at the Physics layer.
