OSI model could be big. I will explain it in TCP/IP model, which is used in modern computersThe TCP/IP model has the following Layers.ApplicationTransportNetworkData LinkPhysicalApplication:When 2 PCs want to communicate they often use an application to communicate. Applications are user interfacing and is in a format understandable by the user.The application layer provides a user with various application services, which a user decides upon the communication. Lets just say PC A wants to send a word document to PC B. Word is an application that a user users at the application layerTransport:This layer multiplexes data. The need for multiplexing, is that there could be many services that would want to communicate with different destinations. This layer in the TCP/IP model, uniquely identifies to the recieving device what application layer program the data sent is destined to.Along with this this layer also provides a user with different reliabilty modes depending upon the protocol usedNetwork:This layer is responsible for logical addressing to identify the network where the reciveing station isData link:This layer is where the data gets another tag with the physical address of the device, to identify exactly what PC the data is destined to in the network identified by the network layer. The physcial address often depends upon the technolgy that you are using (ethernet, token ring, frame relay, PPP etc).Also the data gets split in to series of bits of 0s and 1s and sent to the lower layerPhysical:This is the layer where the data in form of bits recieved from the data link layer gets transmitted in form of electrical signals to the destination