The way I use mods is through forge which can be downloaded by just typing "forge" in your search engine and download it by choosing your version and click the installer button. After you have done that, double-click on it to open it and keep the default options. Next, open your Minecraft launcher and click "Launch Options", click "Add New", click the release option and scroll down to the bottom where you should find "release (version) forge". After you have done all that, name it, click save and click "News" where you can change your version into the forge one and click play. To get mods, download it and then go onto finder and on the menu bar at the top of your screen (put your mouse up to the top of the screen if you are in full screen), click "Go" and then "Go to Folders". Then, paste in "~/Library/Application Support/minecraft" into the box and find the folder "mods". If you don't see the folder make your own (remember no capitals) and drag in the mod (which should be a .jar file) into the mods folder. Restarting Minecraft is required and when you go on, your mod should be on the bar "Mods".