I feel a bit reluctant to help you here, because if you are a total newbie, there are a million things that can go wrong.
So I won't go into all the details.
I am just going to say, you need to make 2 partions on your drive.
If that doesn't ring a bell, than please for your own good, stick with installing one OS at a time and do some extensive research before you go in too deep.
Installing one can be challenging enough.
Greetz
My Computer
At a glance
Win7 Build 7600 x86Pentium II 300MHz32mb EDO RAMDiamond Viper
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics Card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen (VGA)
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 SSD 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0
Sorry, but that is not possible. You cannot have multiple OSes sharing a single partition. Each OS needs its own partition or drive. It is possible, however, to install multiple OSes on a single drive if that drive has got more than one partition (1 per OS, upto a maximum of 4).
My Computer
At a glance
Windows 8.1 Pro RTM x64Intel Core-i5-3570K 4-core @ 3.4GHz (Ivy Brid...4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2...MSI GeForce GTX770 Gaming OC 2GB
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics Card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen (VGA)
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 SSD 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0