Well, you have to make sure to have WinRAR. If you don't have it, you can always download a free trial. Are you actually sure you've putted the files into the right folder. Try by deleting the files, then downloading the same thing and try again.
Maybe some tutorials will help on YouTube, you've probably got something wrong. If you tried many times correctly, but still nothing, you should probably contact the creator of the map/preset/item(s), maybe they could help?
I've only had trouble with items, but now everything is alright. I'm pretty sure your problem can get fixed too.
Here are some tutorials:
-maps: https://www.youtube.com/watch?v=1ULvvPVJIk0 (https://www.youtube.com/watch?v=1ULvvPVJIk0)
-presets: https://www.youtube.com/watch?v=dIFjZ-ww0jM (https://www.youtube.com/watch?v=dIFjZ-ww0jM)
-items: https://www.youtube.com/watch?v=Ew8Mz3mD9ss (https://www.youtube.com/watch?v=Ew8Mz3mD9ss)
-mass markings: https://www.youtube.com/watch?v=b0EpEpcJ_Zw (https://www.youtube.com/watch?v=b0EpEpcJ_Zw)
Now, if you are using Mac, then I'm sorry but I cannot help with that, since I'm only a Windows user. I think there are some differences between Windows and Mac downloads.