I created the partition in Windows 10 (I'm new to Linux, so I used the Windows software I was used to, which wasn't smart of me) and Zorin didn't give me an option to format (it was greyed out) or install the mountpoint. Turns out I had to, when I was in the Zorin installer, I had to delete the 50 GB partition that I'd created (created with Windows), and then when I used the Zorin installer to turn the now 50 GB of hard drive space into a new partition, then I was given the options to format it to ext4, and to install the mount point.
[quote="Leonos, post:4, topic:55889, full:true"]
To create & format partitions, "Disk Management" should be pre-included in Windows and has worked well for me.
You don't need to format the partition to ext4 in Windows though - to do that, and create a Linux mount point, as @NickS says it's probably better to do it from your Linux USB stick![/quote]
Yes, I've just learned to let Linux do the Linux things.
Dual boot with Windows 10. Here is my other thread:
Anyway, this problem has been solved now, in future I will always use Linux to create and use Linux partitions. Thanks everyone.