Coming from a Windows background, you probably wouldn't know this, but Ubuntu (or any Linux system) uses partitions in a different way than Windows does, which is why you're not seeing both the partitions you created.
As you know, in Windows, when you mount a partition it shows up as a drive (C:, D:, or so on), and all the drives are listed under My Computer. Each drive has its own entirely separate hierarchy of files. But Linux uses a different model. In Linux, as far as the operating system is concerned, there is only one hierarchy, which is more or less effectively stored in the kernel's memory. Partitions get mounted by attaching them at certain points in this hierarchy, namely mount points, and when that happens, the contents of the newly mounted partition appear as directories and files under that mount point.
You can think of it as though partitions in Linux provide backing storage for parts of the filesystem.
Here's an example that, while not being 100% accurate, should help you understand how it works. Suppose your two partitions have these contents:
When the Linux kernel starts up, you can imagine that it starts with an empty "mental model" of the filesystem. ("In the beginning, there was
Then it mounts a partition at the mount point
/; let's say that is partition 1. After mounting, the filesystem has these three directories:
Then it mounts partition 2 at the mount point
/home. After that, the filesystem has these six directories:
The net effect of this is that everything under
/home/curly is on partition 2, while everything else under
/ is on partition 1. So, when asked to access a file like, say,
/home/curly/maharajah.txt, the kernel will note that this file is under partition 2's mount point
/home and there are no other mount points "on the way" from
/home to the path of the file, so it will put the file at
curly/maharajah.txt on partition 2. A different file like
/bin/ow, would be placed on partition 1 because it is under partition 1's mount point but not under any other partition's mount point.
But all of this managing mount points is invisible to you, as the user of the computer. In normal day-to-day usage you don't typically care which directories are on which partitions; when you make a file, all you think about is the path
/home/curly/maharajah.txt and you let the kernel worry about which partition to actually put that file on. So, unlike in Windows, partitions are meant to be invisible during normal use, and you work with the illusion that there is only one big filesystem that contains everything on the system. Some file managers, like Nautilus apparently, help promote that illusion by not even showing you what partitions are mounted.
What this means for your specific situation is that you (probably) already have things set up the way you want. Your 50 GB partition is mounted on
/, and your 410 GB partition is mounted on
/home, and that means anything you create under
/home will be placed on the 410 GB partition while everything else on the system will be placed on the 50 GB partition. (Well actually there are other "imaginary partitions" created by various Linux system components, but forget about that for now.) It's just that Nautilus is not making it very clear that both partitions are being used, and in fact being kind of misleading by showing the space usage for only partition 1 in the "other locations" screen.