Best practice is to install Windows 1st on a set partition size then Linux to take the rest, as the other way around would require a higher skill level.
I would highly recommend you read a book like
Linux for dummies maybe you can source a copy from a friend <hint, hint> To get a grip of what it is. Its totally different in how it handles programs, hardware and such, ie: there is no such thing as C: D: and Program Files.
Edit: oh and gparted can shrink partitions. best practice is to mount / as one partition and /home as extended. Using another drive as NTFS that both windows and Linux can access for all your other stuff like movies and so on.