This is how to install mcp56 so you can make mods for a mac and windows!
It's very easy!
Get mcp at this link.

Windows;

1. Dowload Mcp56 or other versions you have.

2. Put an unmodified bin and recourses folder in your mcp jars folder

3. Run the decompile.bat

4. Create your mod

5. After you make your mod, run the recomplile.bat

6. After you recompile, run the startclient.bat to test

7. After you test, run the reobfuscate.bat to create the code files.

Macs;

1. Dowload Mcp56 or other versions you have. (same as windows)

2. Put an unmodified bin and recourses folder in your mcp jars folder (same as windows)

3. Open Terminal

4. In Terminal, type; cd, then you drag in the mcp56 folder into Terminal, then you type bash, add a space, then you drag in the decompile.sh, then press enter!

5. Wait for it to decompile.

6. Create your mod in the src folder. (you need to go through many folders! The final folder is src. Just like the beginning!)

7. After you create your mod, in Terminal type bash, add space, and drag in the recompile.sh, then press enter.

8. After that, to test it, type bash, always add a space after bash, drag in the startclient.sh then press enter! It will open a minecraft for you to test.

9. After you test it, type bash, then drag in the reobfuscate.sh, then press enter. It will make the code files.

10. (for both macs and windows) Make a folder, and put your files in your folder.

That's how you setup mcp! Watch the video if you want!