How do you use a post reticle scope?

[High Tower]

I just traded on an Marlin 36 30-30 with a Weaver K-3 scope that has a post reticle. I have never used this before and am not quite sure how to sight it. My question is this. The target/point of aim goes on top of the post and disregard the horizontal line or line up the horizontal line with the post which may mean the cross section is below the top of the post. Right now the horizontal line is below the top of the post. Any help is appreciated.