Agree - sfdisk has it's uses (*mighty* good ones), but this may not be one for a presumably new user.
That looks like something from the man page. This might work for you
sfdisk /dev/sda << EOF
Personally I think you should consider cfdisk - it's "graphical" (in a sense
), and you see what you are doing. Use the up/down arrow keys to highlight the free space, then left/right arrows to select the commands along the bottom. "new" to create a (primary) partition - just take all the defaults for size, start.
"write" to update the partition table, and "quit" to get out.