This tutorial provides the basics for using a WIZ5500-based Ethernet Shield with an Arduino compatible. The Wiznet WIZ5500 is a modern Ethernet interface chip and is used in the Ethernet Shield W5500 and the Feather Ethernet Wing available at Adafruit.
The shield form factor works well for ATmega328 based Arduino compatibles like the Arduino Uno R3 and the Adafruit Metro 328 (Classic). The shield contains both an Ethernet connection for networks and an SD Card slot for storing data.
The Feather wing works well with a Feather with a SD card slot. The Feather 32u4 Adalogger has an Arduino Leonardo compatible 32u4 processor and a micro-SD card slot. With the Ethernet Feather Wing, it provides the same functionality as the Ethernet Shield+Metro/Uno in a much smaller package. SD and micro-SD are the same for all purposes but the latter is smaller. In this tutorial, when it says do something to an SD card and you are using the Feathers, think micro-SD.
This tutorial assumes you already know the basics of the Arduino IDE, code generation and the Arduino interface. If you are not so familiar with the Arduino IDE, you might check the tutorials in the Adafruit Learn Arduino Series.
As of the date of this revised tutorial, Arduino notes their Ethernet Shields are retired. If you use a retired or third-party Ethernet shield, you may have to use a different Arduino library that supports the chipset the board uses.
Note that the Ethernet Shield and Feather Wing Adafruit uses is based on the WIZ5500 chip, not the older WIZ5100 chipset or others. The WIZ5500 requires the Ethernet2 library, not the older Ethernet library on Arduino. If you use the older hardware, just be sure you change libraries back from Ethernet2 to Ethernet and double check things.
This tutorial will go through preparing then using the SD card, both in general then reading the files on a card. The final example will show how to access the SD card remotely over Ethernet. This capability could be the basis for a remote file storage or other program that access a remote Arduino compatible.