First, you will need to checkout the sourcecode from Subversion. It's easy to do this; just install "Tortoise SVN" (or any other SVN client) on your system, and instruct the client to check out all sources from: https://svn.apache.org/repos/asf/myfaces/current.
You do not need to use https if you do not want to commit anything to the sourcebase, if you might want to do a commit at some point, it is recommended to use https as a protocol right away.
How to build MyFaces in your IDE
For debugging and extending MyFaces, you might want to get the project up and running in your IDE. For this purpose, we have set up the instructions for doing so on this page.
Choose your IDE
JetBrains_IntelliJ_IDEA - Using MyFaces in IntelliJ IDEA
Eclipse_IDE - Using MyFaces in Eclipse
Getting_started_with_Netbeans_and_MyFaces - Using MyFaces in Netbeans
GettingStartedWithNetbeans - Using MyFaces in Netbeans (Dutch)