This guide is based on the information given at raspberrypi.org.
First download the full image of raspbian jessie latest raspbian.
At this time it is the 2017-04-10-raspbian-jessie.zip.
Extract the .img file.
If you use windows, you can download the Win32 Disk Imager.
After installed and started the Win32 Disk Imager you see the following screen:
Select the correct Image file and the Drive (e.g. F:\) and press “Write”.
After process is completed, you can insert the sd card into your Pi and start the system.