The RedHatLinux text interface and graphical interface conversion problems.

The RedHatLinux text interface and graphical interface conversion problems. -- Linux general technology-Linux technology and application information. For details, refer to the following section. Hello everyone, I am a student at school. I have been in contact with Red hat for more than half a year. I think it is very good.
Last week, the teacher taught us a way to go back and forth into the text and graphic interface, that is, to use the Vi text editor to change a file that can enable red hat to enter the text or graphic interface.
However, I did my experiment in class and failed to write it down completely, as if I had changed a file.
Who can help me remember it.
The younger brother waits for answers online.