As with many other related questions: it depends...

It depends on what is your goal or purpose to use Linux. To use it as a fully-featured desktop system with all the bells and whistles, you'll need much more space than using it as a server without a fancy graphical desktop and other desktop applications (LibreOffice, web browser etc.). Usually during the installation procedure you can choose which components / applications you would like to install, so you can adjust the installation to your exact needs.

Ubuntu suggests 25GB storage space for a typical desktop installation, and 1.5GB for using it as a server (the bare system, without your data). Embedded systems can do with much less space , e.g. Linux based WiFi routers usually contain pretty small root filesystems, typically 8-16-32-64 MB (most of the time these devices use a compressed filesystem, e.g. cramfs).

It is advised to install the system on its own separate disk partition, but in case it is not option for you, you could try e.g. Wubi (Windows-based Ubuntu Installer) to use your existing Windows partition without destroying it (can be a huge advantage if you're just testing). The drawback is that your Linux system will run slower because of the additional filesystem mapping layer.

BTW, I remember creating a custom system back in the old days, which booted the Linux kernel from a 1.44 MB floppy disk, then used a 32 MB (sic! megabytes) USB flash drive as the root filesystem. And it still had some free space for the system logs...

Dear David V.

Thank you so much for such a great information. My purpose of use is only to run the JULIA ATOM siftware. which I tried to run in Window 10 but all struggles seems just a vain nothing more. Therefore it was suggested to run use Linux. I never used it. So your detail answer can helo me in this regard.

Try to install the Linux distribution of your choice using VirtualBox or VMWare on your Windows box.