You can create a bootable USB flash drive to use to deploy Windows Server 2012 Essentials .
The first step is to prepare the USB flash drive by using DiskPart, which is a command-line utility or you can use the software to automatically burn the os to udb.
To create a bootable USB flash drive manually
Insert a USB flash drive into a running computer.
Open a Command Prompt window as an administrator.
In the new command line window that opens, to determine the USB flash drive number or drive letter, at the command prompt, type
list disk, and then click ENTER. The
list disk command displays all the disks on the computer. Note the drive number or drive letter of the USB flash drive.
At the command prompt, type
select disk <X>, where X is the drive number or drive letter of the USB flash drive, and then click ENTER.
clean, and the click ENTER. This command deletes all data from the USB flash drive.
To create a new primary partition on the USB flash drive, type
create part pri, and then click ENTER.
To select the partition that you just created, type
select part 1, and then click ENTER.
To format the partition, type
format fs=ntfs quick, and then click ENTER.
To create a bootable USB flash drive Automatically
Now you can create bootable usb pendrive or also you ca make your sd card also a bootable device using the tool called as Rufus
Download the Rufus Software using above link ,open and you can see option to select iso image of your operating system,simply select it and choose the pendrive that you want to burn it,them done start and wait for the completion of burning process.
After completing ,now you have bootable usb drive.