Download the ISO for the installation DVD (typically from the MS VLSC) such as the Windows 2012 R2 DVD ISO.
I recommend that you boot up the server and go through RAID configuration using Control - R to set up your RAID array before continuing. RAID is not configurable inside Windows setup.
Open the DRAC web interface (default location is 192.168.0.120 with a username/password of root/calvin).
Open a virtual console.
In the virtual console.
Click Virtual Media -> Connect Virtual Media
Click Virtual Media -> Map CD/DVD
Choose the ISO file from your local machine (the ISO file should be located on your phsyical machine - not at all on the server). I highly recommend you do this over a wired connection. It'll take 20+ minutes over a wired connection to transfer the contents of a 6 GB ISO file and more than an hour over wireless.
In Next Boot, choose virtual CD/DVD/ISO.