Why are you so difficult to downgrade in Linux?

Linux: How are you so difficult to downgrade-Linux general technology-Linux technology and application information? The following is a detailed description. Author: Leng Yue wordless
Two days ago, the mentor would like to write a Linux User Guide, so that we can familiarize ourselves with the Linux system and help us with this guide. It's easy to think about it. windows is a small case, think about something that has never been done before. But who knows it has been annoying for this system for the past two days!

If you have no CD, you can only install it from the next image on the Internet, but the system will have 3 GB of capacity. If you do not need to install a Linux system on a windows system, first, the premise is that the disk in windows must be in the fat format, and my system was in the Ntfs format. At first, I didn't understand what happened. Why can't I install it on the Internet, later, I realized this was the problem, so I had to be reluctant to reinstall my windows system. Later I learned that Linux was installed on my computer. This is not a headache, but the next thing makes me difficult.

First, the Linux system is a new generation of things for me, but I don't know where to start it. I don't see the directory partition or the system is under that door, and the software has never been installed. I have never seen things on QQ for a day. I can't play songs, listen to movies, watch movies, or access the internet, later, I wanted to change the system back, but the Windows system CD in Linux was not recognized. I said I needed to format the hard disk on the Internet, so it would be no big deal, but now I can't find how to solve it. This system is so stubborn that I cannot conquer it. What should I do?

I am grateful if my fellow citizens can solve this problem!