Hi, welcome.
You have prompted me to do something I should have done a while back. ekc posted a script a few weeks ago designed to automate/simplify the whole mods installation and enabling process. So I figured we need a simple step by step description of how to use it. And here it is. It will only work with the Steam version of Civ5, and mods you can Subscribe from Steamworks.
Step 1. Download the attached Applescript, which is a modified version of ekc's original script. It downloads as a zipped file, and you should unzip it and put it in a location where you can find it again, e.g. your desktop.
Step 2. Open Steam and click on Steamworks. Choose the mods you want, and click Subscribe for each one. They will download to a hidden location on your Mac.
Step 3. Run the script you installed at Step 1 by double clicking it. This will edit your Civ5 software to enable the Mods menu option, and extract the mods you subscribed, and place them in your Civ5 Mods folder.
Step 4. Launch Civ5 from the Steam window. Click the Mods menu option and accept the "Use MODS at your own risk" warning.
Step 5. Enable the mods you want by checking their tick boxes in the list. Click Next and wait for the Game to Configure. Click Single Player at the top of the next screen, then Setup Game. Choose the settings for the mod. These will depend on the mod(s) you have enabled.
Step 6. Play the game.
You can repeat Step 2 later to download more mods. Run Step 3 each time to install the new mods.