Measure the width of the window frame you want to hang your curtains on.
Purchase a magnetic curtain rod set from your hardware store or online.
Attach the magnetic rod to your metal window frame as per the manufacturer's instructions. Use a bubble level to make sure it's level.
Hang your curtains on your new rod.
Purchase a curtain rod that's long enough to be fitted to the wall above or beside your window frame. Make sure it will accommodate curtains that are wide enough to cover your window.
Drill screw holes for the brackets of your rod into the wall above or beside the top of your metal window frame. You'll need the appropriate drill bit for the material your wall is made from.
Put up your rod and hang your curtains as per the manufacturer's instructions. You can use wall filler to disguise the holes you've made should you decide to take your curtains down.