Start by installing the OS on the MicroSD card, either NOOBS or Raspbian, both provided by the Raspberry Pi foundation, available on their site. NOOBS, which stands for New Out Of Box Software, is designed for beginners, and is the easiest to install on your SD card. You can either follow their official instructions, or see below.
Format the SD card with a single partition of FAT32, using either the system drive management tool or a third party tool, such as the SD Association's SD Formatter 4.0, or GParted. Download the NOOBS ZIP file and unzip it. next, copy the files over to the partition that you just created. Ensure that you eject it before disconnecting it.