If you want to install Ubuntu in dual-boot with Windows, the best way for a beginning user is:
- Install Windows on a partition using 40% of your hard disk
- Install Ubuntu on a partition using 40% of your hard disk
- create a FAT32 partition of 10% of your hard disk
- Leave the other 10% space free for now to allocate it later to wherever you will need it.
Then:
- When you use Windows, use your Windows applications on your Windows files
- When you use Ubuntu, use your Ubuntu Applications on your Ubuntu files.
- When you need files accessible to both Ubuntu and Windows, store them on the FAT partition.
Never any problems!