Problem with $INSTALL_PREFIX

Im trying do build gvm.

mkdir -p $BUILD_DIR/gvm-libs && cd $BUILD_DIR/gvm-libs


And i do :
cmake greenbone/gvm-libs-22.4.4 \


and my output is, really cant understood how $INSTALL_PREFIX works.

CMake Error: The source directory “/home/spears/buildgreenbone/gvm-libs/greenbone/gvm-libs-22.4.4” does not exist.
Specify --help for usage, or press the help button on the CMake GUI.

I think i do mistake in this too.
export SOURCE_DIR=$HOME/source
mkdir -p $SOURCE_DIR

Can someone help me get throught the variables with $?