I installed Ubuntu along with windows 10.when I install it,I chose "something else" and installed.Because i wanted to have separate '/home' partition.But i cant view that home partition as a separate partition.It appears as a folder inside the "files". But i can view my other two windows partitions as separate partitions in side panel ?

Output of cat /etc/fstab:

# 
# Use 'blkid' to print the universally unique identifier for a 
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5). 
# 
# <file system> <mount point> <type> <options> <dump> <pass> 
# / was on /dev/sda5 during installation 
UUID=924e32ac-04aa-4b15-a7cd-420fa259f826 / ext4 errors=remount-ro 0 1 
# /home was on /dev/sda6 during installation 
UUID=8d775a19-adf1-4064-a0c4-9d2a7b3ed638 /home ext4 defaults 0 2

This is normal

Ubuntu, and Linux in general work differently from Windows. In Windows, partitions show up as C:, D: etc. In Ubuntu partitions are mounted into empty directories or folders.

Automatically mounted partitions

Some partitions are mounted automatically when the system starts. This is governed by the file /etc/fstab. In your case, two partitions are mounted automatically, the / partition, also known as the system partition or the root of the file system. The other is is the /home partition. Once the /home partition is mounted, the home folder under the / partition becomes the /home partition. This partition has your Home sub-folder such as /home/username`. Anything you put in your Home folder goes directly into the partition.

In your case, the /home partition is mounted at the /home folder. When you installed Ubuntu, and assigned /home as the mount-point for the ne partition, the installation process set it up so that the partition is automatically mounted at that mount-point every time the system starts. That's why you don't see it as a mountable partition inside Nautilus, also known as Files app.

The partitions that are automatically mounted at system startup are governed by the file /etc/fstab. You can see the contents of /etc/fstab by opening a terminal by pressing Ctrl+Alt+T and entering the command:

cat /etc/fstab

If you see a line with /home in it, then your /home partition is mounted at that folder when the system starts. It has to be done this way. Otherwise you will not be able to use the partition as your /home folder.

Other partitions not mounted by default

You have two other Windows partitions. These partitions are not mounted automatically when the system starts. Your /etc/fstab file does not have any reference to these partitions. Therefore, they show up as drive icons on the left panel of the Files app. When you click on one of them they will be mounted on a temporary folder. Inside that folder, you will find all the sub-folders of that partition. To unmount such a partition, click on the Eject icon next to it on the left panel.

If you want to mount your Windows partition at system startup, you will have to create a mount-point folder (or select an existing empty folder) and edit the /etc/fstab file. For example, if I want a separate partitions for my music. I can create and format a partition. Let's call this partition /dev/sda6. In Windows, the partition is given a new letter name, such as E:. This does not happen in Ubuntu. In Ubuntu you have to mount a partition to a folder so that you can use it. In my case, I want to mount this partition in the folder /home/myusername/Music. This Music folder already exists. If if didn't I would have to create this folder. Then I can mount (think it as assigning) this folder to this partition. This folder is then called the mount-point for this partition.

You don't have to do anything. Everything is working normally.

Hope this helps

If you don't want your windows files to show in Ubuntu:

Then you would have to encrypt your windows partition using windows 10 system programs or third party apps. However, the encryption will be performed using your Microsoft account credentials as key. Assuming you didn't have the option to select "encrypt whole disk" when installing Ubuntu (or maybe you just encrypted just your /home folder), your Ubuntu files will also be visible in windows.

Generally speaking
We can't expect the operating systems to have been designed to work alongside each other. Keeping this in mind, I don't recommend dual booting unless you absolutely have to.