These lightweight metal U-shaped curtin rods engage those hooks. The uprights of the U are maybe 3" or 4" long and the base is straight and whatever is needed to span the window. The rod is pushed on while angled upward then pulled horizontal. There is a hole in the upper apect of the rod which the top hook protrudes through. The curtain rod is in two parts one of which slips inside the other to allow width adjustment.

You *might* have to scrape paint off the hooks for them to properly engage. Depending on the span of the widow these rods may need one (or more) supports in the middle. The usual supports are metal hooks which screw into the header above the window. Usually these come in the parts package accompanying the rod. 

[![lightweigth curtain rod][1]][1]


  [1]: https://i.sstatic.net/crFrF.png