To install QUANTUM ESPRESSO from source, you need first of all a minimal Unix environment, that is: a command shell (e.g., bash, sh) and utilities make, awk, sed. In order to install external libraries from scratch, you will also need git v.2.13 or later. For MS-Windows, see Sec.2.9.4. If you prefer installation with CMake (supported since v.6.7), you will need a recent (v.3.14 or later) working CMake software; otherwise you will need the configure command from autoconf and, for FoX compilation, m4.
Note that the scripts contained in the distribution assume that the local language is set to the standard, i.e. "C"; other settings may break them. Use export LC_ALL=C (sh/bash) or setenv LC_ALL C (csh/tcsh) to prevent any problem when running scripts (including installation scripts).
Second, you need a Fortran compiler compliant with F2008 standard. For parallel execution, you will also need MPI libraries and a parallel (i.e. MPI-aware) compiler. For massively parallel machines, or for simple multicore parallelization, an OpenMP-aware compiler and libraries are also required. To compile for GPUs you need a recent version of the NVidia HPC SDK (software development kit), formerly PGI compiler, freely available for download.
As a rule, QUANTUM ESPRESSO tries to keep compatibility with older compilers, avoiding nonstandard extensions and newer features that are not widespread or stabilized. If however your compiler is older than a few (∼5) years, it is likely that something will not work. The same applies to mathematical and MPI libraries. For GPU compilation, you need v.19.10 or later of the NVidia HPC SDK (previous versions are no longer supported).
Big computing centers typically provide a Fortran compiler complete with all needed libraries. Workstations or ``commodity'' machines using PC hardware, may or may not have the needed software. If not, you need to buy a commercial compiler or to use the open-source gfortran compiler from the gcc distribution (and possibly MPI libraries and run-time software). Note that most commercial compilers are also available free of charge under some conditions (e.g. academic or personal usage, no support) and may provide MPI libraries and run-time software as well.