vi insertion question

[Ned]

HI list,

I am trying to insert a line in a document with vi.
Precisely, I need to insert that line to be the first one in the document.
How can I turn on/off the insertion mode in vi?
Acording to instructor, we have to use the escape key to get out of the insert mode for every new line.
How can I switch btw the modes in vi and how can I know in what mode is the program at?

Many thanks!
Ned