'>' is output redirection and
'<' is input redirection.
For eg: dir > dir_file
The output of this command will not be displayed on screen. it will be stored in dir_file.
the difference b/w > and >> is, the last one appends the results with the previous contents.
eg: dir >dir_file (dir_file created with directory listing)
tree >> dir_file (the output of the tree command is appended to the dir_file.)
but if we sue tree > dir_file the previous contents will be lost.
In DOS, even if you redirect the output, error messages will be displayed on screen.
But in unix, linux shells, you can also redirect error messages to files.