Pick a folder in which which the code is to be downloaded to, let's call it "Code".
First, make sure you have these packages installed:
git
autoconf
libtool
You can install packages running this command:
sudo apt-get install [package name]
To download the source (from within the "Code" folder):
git clone https://github/goatpig/BitcoinArmory.git
cd BitcoinArmory
git checkout testing
git submodule init
git submodule update
To configure the project (from within the /Code/BitcoinArmory folder):
The configure script may fail, telling you you are missing certain packages. In this case, you want to install the package, using apt-get.
Finally to build and install (still from the same folder):
make -j8
sudo make install