Why we are using Redsnow Recovery fix option ? Answer is in this name, we are using this Recovery Fix option when errors occured iOS downgrade and recover to that issue. When we are downgrading iDevice into lower version using iTunes some moments errors are occured. In this situation we can recover this issue using Redsnow.
This Youtube vidoe form iDownloadBlog, It is clearly shows how to fix recovery using Redsn0w.
We can go to recovery fix by clicking extras button. Then following windows will apper. You need to set device as DFU mode when you are doing Recovery Fix using Redsnow.
Next window, You need to set the Device into DFU mode. I think you already know this..