for sharpening a knife I prefer an oilstone. Its not really something that can be told by description- its best taught. And even then people have their favourite way of sharpening. A lot depends on the angle of the cutting edge of the blade- yes- it does have an angle!!There are loads of websites you might care to trawl through which may help you but often getting on and trying it out is the best way- providing you have an old knife or two you dont mind experimenting with!
Fles are essentially an abrasive surface and can't be sharpened - a bit like one of those green scouring pads. When it's worn out you have to replace it.
Your file may have old shavings on the 'teeth' if it has been used on soft metals. It can be cleaned with a steel brush, but no, you can't sharpen them.