I'm trying to follow the Bare Bones tutorial on the OS Dev wiki but I'm confused on how to build the GCC cross compiler. It says to install the source code for stuff like bintuils, GCC, GNU GMP etc, but most of it is already installed or can be installed from the software center. Do I need to install a second copy? It also said to install into $HOME/opt/cross, but I could only find /opt, and I'm assuming "cross" is a directory I'll have to make. I've never built anything through source code before, only installed from PPAs. I'm doing this for a class project.
mkdir -p $HOME/opt/cross will create the directory, where you should install your cross-compilation tools.
sudo apt-get install apt-src;man apt-src will show you how to get the source code for any package.