A network is a group of IP addresses.
Network configuration for each host (device) depends on the ip and subnet mask => network ip.

Sockets and the socket API are used to send messages across a network. A socket is the software component to enable the communication between processes working on two physically separate machines. From an application point of view, it is a particular object on which to read and write the data to be transmitted or received.

a socket is the 'standard interface' to connect common 
electronic devices to the home electric network

    SOCKET         PLUG
     _____        _______
____|     |>>>>  | _ | _ |
____|     |      ||_|||_||
    |_____|>>>>  |___|___|

socket()
bind()
listen()
accept() // server accepts client connection
connect() // client establishes connection \

send()
recv()

close()

The three-way handshake is important since it ensures that each side of the connection is reachable in the network, in other words that the client can reach the server and vice-versa. It may be that only one host, client or server, can reach the other.