Streams?

I'm really confused about how to load data from a text file. I can't seem to find any examples. And what's the deal with streams? What is it?

' readstream.bmx

' opens a read stream to the blitzbasic.com website and
' dumps the homepage to the console using readline and print

in=ReadStream("http::blitzbasic.com")

If Not in RuntimeError "Failed to open a ReadStream to file http::www.blitzbasic.com"

While Not Eof(in)
	Print ReadLine(in)
Wend
CloseStream in

taken from Community Docs .
<edit> Obviously, instream should be declared as type TSTream.