First, you need both a Micro SD card and a Micro SD card reader. Many modern computers come with a Micro SD card reader built-in. The SD card must be 4GB or larger and preferably Class 10 or better.
Next, you need to download the Screenly disk image. The process of writing the Screenly disk image to an SD card is the same regardless of whether you are trying to install Screenly OSE or Screenly Pro.
In the video below, you can follow the process from start to finish.
That’s it. Now you can simply put the SD card into your Raspberry Pi, and Screenly will boot.