I've looked at that but I get an error message that says:
"No root file system is defined.
Please correct this from the partitioning menu."
I'm sure not where to add the root file system though?
Sorry for sounding thick but I don't want to mess up my other partition because it's got all my data on it and want to get this right first time.
Here's a screenshot, well sort of, for some reason it cuts off half of it but you can still see what I mean, it's most probably really easy but I don't want to do the wrong thing.
Linux Mint 17.3 (Cinnamon) 64bit.