The standard way of using a Raspberry Pi is to run the OS from a micro sd card. The problem with this is that the SD Card has limited read and writes, which will cause the SD to fail in a short period of time, especially if you write to files frequently. This started to become a problem for me when was running a monitoring script which wrote to a file every 10 mins. After seeing SD Card failures I opted to move the OS to a USB and run off the usb just like you can on a full computer. The following instructions are written with the intent of being carried out on windows, but the instructions are similar for all platforms but you may need to use different tools, for instance if I was to do this on Ubuntu I would use the Disks application for the formatting of the drives and UNetBootin to write to the USB and SD card.