How to make filesystem on unallocated space in windows for ubuntu 20.04

I am trying to solve this problem here following steps here and someone suggested the following to me

The installer may have expected you to make a partition on the free space, before you went into the install step. Most installers force you thru this step. You have to 1. make a partition, 2. put a filesystem on it, usually ext3 or ext4, and 3. give it a mount point name (eg /). You usually need to make a minimum of a root filesystem partition ( called /), and a swap partition. So when you did step 4, you only made free space, not a partition.

unallocated memory see here

Would someone shows me how to make this unallocated memory partition of the filesystem?

To make a partition and file system yourself, you use disk partitioning software, either in Windows or in an Ubuntu live session. However, if you are going to install Ubuntu the installer will take care of that.

A very good tutorial for Ubuntu 20.04 with screenshots is available over at Itsfoss. Of course, the ultimate reference remains the official documentation.

If you select the option "Install Ubuntu alongside Windows", the installer will allow you to shrink the Windows partition to make space for a linux partition. However, if you do not see that option, then you must create and assign partitions manually from within the installer by selecting "Something else".

• The easiest is the option "Install Ubuntu alongside Windows". If you already have the free space, there will be no need to further resize the Windows partition. You just hit Install Now on the "Install Ubuntu alongside Windows Boot Manager" screen, and the system will automatically create and format a single root partition to install the system. Swap is implemented as a swap file, not a separate partition nowadays.
• Else, if you do not see that option, you need to select "Something Else". You then need to create a partition yourself in the free space. While the tutorial shows how to set up a separate swap space and separate partition for /home, you can, for simplicity, also just stick to a single partition. Once you assigned the partition, a click on the Install Now button will automatically create and format the partition.