trouble moving plugin download in my macintosh

I would like to know why I am unable to complete the downloading process of a plugin from the web to my wordpress 3.7.1 plugin library.

I am successful at downloading the plugin and I see it in the mac’s downloads but when click on choose, it simply opens up the folder, showing me files and more folders with the download folder. It does not make the final step of moving over into the 3.7.1’s plugin library

I think the problem lies with my not completely understanding the macintosh OS download process. If I was using a Windows system it would already be done

Thank you very much