Here are answers to your questions.
IP Address : IP stands for Internet protocol. The address generated by the device while connecting to the network remains unique to the device. Depending on the device choosing static and dynamic IP. You'd find that the number either changes per router reset or it remains the same for connected device connection.
Digits of IP
IPV4 address size is of 32 bit. And first 2 set of the IP represents the either binary, hexadecimal and octal numbers. Depending on the number set by your ISP. Rest of the set represents the connection and the device. As the maximum allowed numbers for the IPV4 are now exhausting and do not cover more devices anymore. The IPV6 was developed to address this issues. In case of IPV6 the number represents the unique local address followed by the network type, network connected and other information.
Accessing information from device
Server talk to each other in terms of packets. And are recognized on the basis of IP. So when one server sends the data to another. The log gets registers for the origin of packet. That's how the unique transfer of the data is being shown to the devices from one end to another.
Identification of Device from IP
When any device gets connected to network, it automatically gets assigned the IP address. You can find out the IP of the device from many ways.
Open command prompt and type ipconfig. And this should show you the IPV4 address at the bottom of the returned query.
As an alternative, if you google "what is my ip" then google will return you the IP Address information back.
Apart from this, there are some small apps available in the store that can show you that information.