When you installed SMAPI did you identify the path to the mod folder to which all your mods go?
If you used the default location (i.e. you didn't pick your own location) you can find the appropriate path by:
- Clicking "Go" at the top menu ribbon
- Click "Go to Folder..."
- Put in the appropriate path as seen on the main "SDV Modding: Getting Started" page (See under "Find your game folder - Mac" for the right path for you as i don't know if you use Steam or the other option, GOG).
It's true that when you try to click your way through to the SDV contents folder as you did, it doesn't show up, but doing it this way, should get you to the Mod folder (just verified on my mac to make sure). I would recommend that you add it to your "Favorites" menu so you can easily get to it in the future.