In order to install WEST you need to download the latest Quantum Espresso release .
Quantum Espresso (QE) is an integrated suite of Open-Source computer codes for electronic-structure calculations and materials modeling at the nanoscale, based on density-functional theory (DFT), plane waves (PW), and pseudopotentials (PP).
Configure Quantum Espresso by running the configure script that comes with the QE distribution. WEST requires MPI support (Scalapack and OpenMP support is also recommended, but optional). If all the environment variables (compilers, libraries etc.) have been set according to the QE configure guide, this would simply be:

cd QuantumEspresso_dir
tar -zxvf West-3.0.0.tar.gz

It's now time to create the pw.x, wstat.x, wfreq.x, and westpp.x executables by doing:

cd QuantumEspresso_dir
make pw
cd QuantumEspresso_dir/West

You have succefully installed QuantumEspresso and WEST if you see the executables pw.x, wstat.x, wfreq.x, and westpp.x created in the QuantumEspresso_dir/bin directory.

> ls QuantumEspresso_dir/bin/
... (other content) ...

Congratulations, you are all set for running Quantum Espresso and WEST!