The Physical Layer is where we finally transmit our data. It is also when we initially receive data.
When we send data, we translate frames into bits and transmit them through the respective medium, be it twisted pair, fiber optics, or coaxial.
When we receive data, we translate the bits received into frames and then process the data upward in the OSI model.
The Physical Layer is probably the most basic of all the layers in the OSI model, yet it is still just as critical.