You have two options for operating systems available directly from Raspberry Pi; NOOBS and Raspbian.
NOOBS is the New Out Of Box Software which contains several operating systems accessible via an easy to use launcher.
Raspbian is the full Raspberry Pi operating system.
I have opted to use NOOBS for my micro-SD card as it includes a recovery console (hold down the shift key during boot). Download NOOBS from the Raspberry Pi downloads page. Click the large NOOBS image:
I opted for NOOBS Lite as my Raspberry Pi has a network connection available.:
Choose a download location and save the file.