Expand Ethernet interface intro

docs/reference/api/connectivity/networksocket/EthInterface.md

@@ -1,19 +1,45 @@
 ## Ethernet
 
-The EthInterface provides a C++ API for connecting to the internet over Ethernet.
+The `EthInterface` provides a C++ API for connecting to the internet over Ethernet. By default, this class does not require any configuration. It is able to pick up the default Ethernet driver for the target and select the correct network stack.
 
-### EthInterface class reference
+### Usage
 
-[![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_eth_interface.html)
+To statically initialize the driver, create an object without passing any parameters:
 
-### Usage
+```cpp
+EthernetInterface eth;
+```
+
+Then, if the default configuration is enough, bring up the interface:
+
+```cpp
+nsapi_error_t status = eth.connect();
+```
+
+Now, the interface is ready to be used for [network sockets](/docs/development/reference/network-socket.html).
+
+```cpp
+// Open a TCP socket
+TCPSocket socket;
+socket.open(&eth);
 
-To bring up the network interface:
+// Open a UDP socket
+UDPSocket socket;
+socket.open(&eth);
+```
 
-1. Instantiate the `EthInterface` class.
-1. Call the `connect` function.
-1. Once you connect the EthInterface, you can use it as a
-target for opening [network sockets](/docs/development/reference/network-socket.html).
+### Configuration
+
+For EthernetInterface, there are two possible configurations:
+
+- Use DHCP for network addressing. This is the default.
+- Use statically configured IP addresses.
+
+Refer to the API below for how to set the IP addresses by calling the `set_network()` function.
+
+### EthInterface class reference
+
+[![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_eth_interface.html)
 
 ### EthInterface examples