You will need the following:
Note: MultiMC will download as a zip file. You need to extract that zip file. You can double click on the zip file and drag the MultiMC folder to your desktop. This installs MultiMC to your computer. To open MultiMC, just open that folder, find the application and double click on it to launch it.
Now you're ready to install your modpack. Here's how to do that.
1. Create a new instance for your custom modpack. By clicking on the new instance button as the image below shows you.
2. Name your modpack something and then click the "..." beside the version to set the version according to what our modpack representative tells you. If your modpack rep told you to use version 1.6.4, then choose 1.6.4.
3. Click on the "edit instance" button.
4. Click on the "install forge" button.
5. Select the version of forge that your modpack representative as told you to use like the image shows. In this image, our rep told us to use forge version 965.
6. Then click on "loader mods".
7. Click on the "add" button.
8. Browse on your computer to the unzipped custom modpack on your desktop. And select all of the mods. You can do this easily by using the ctrl + a keyboard shortcut.
9. The mods will appear. Next click on the "settings" place like the image below describes.
10. Click on the "Memory" checkbox and set your PermGen to 128 or higher. Note: the more mods you have the more permgen you will need. Increase it if you get an error in your console that says "max permgen reached" or similar.
11. Go to your desktop and open your unzipped modpack and click into the configs folder. Then on MultiMC click on the "Config Folder" button. A folder called "config" will open.
12. Select all of your configs using ctrl + a and drag and drop them into your custom modpacks config folder like the image shows. They should all move to your custom modpack's config folder. You can now exit out of both of these windows.
13. Go back to MultiMC program and double click on your custom modpack to launch it!
Note: It may take a little while for the modpack to launch if you have a lot of mods. You will have to use MultiMC to run your custom modpack on your computer from now on.
If your modpack contains Flan's mod, follow these instructions after installing your mods:
1. Open MultiMC, and right click the Minecraft instance you are going to install the modpack to. Click "Instance folder".
2. Open the minecraft folder in the new window that pops up.
3. Open your modpack zip file.
4. Drag the Flan folder from your modpack into the Minecraft folder.
5. Start the Minecraft instance you were just working with and connect to your server.