So I have an Windows 10 computer, a VGA/HDMI cable, and an Ubuntu 16.04 HP Laptop. Is there any way to use my laptop as a second screen to my Windows computer, but still see Ubuntu UI and all that? Like to have a window opened on Ubuntu seeing my Windows computer.
I don't want any remote software like TeamViewer.
You will most likely need software to accomplish this. Synergy will allow you to share the mouse and keyboard, which would make it feel somewhat like the same machine.
http://synergy-foss.org/