This is a tutorial on how to install Optifine onto Minecraft using OS X (Mac)
Step 1: Going to Optifine.net
Using the Browser of you're choice go to optifine.net, I will be using Bing.
Step 2: What to Do Once on Optifine.net
Once you are optifine.net select Downloads.
Step 3: What to Download
You can Download any version of Optifine you want. Just make sure it will work with you're computer and the version of Minecraft you want to use it on. I will be using 1.8.9 Optifine HD Ultra HD U H3. When You selected the version you want click (Mirror).
Step 4: Downloading Optifine
To download Optifine you will need to select the version of Optifine you chose between the two adds.
Step 5: Open You're Download
On you're Dock open the downloads folder and select the Optifine .jar file.
Step 6: Installing Optifine
To install Optifine select the install button.
Step 7: Opening Minecraft
Once Optifine is installed you will need to open Minecraft then you are all ready to play!