Recently discovered this site https://hpc-wiki.info/hpc/HPC_Wiki, which gives some useful introductory info to those wanting to learn how to program a supercomputer (or just curious about the process).

For example, here https://hpc-wiki.info/hpc/MPI is an intro to one parallelization architecture, called MPI, and here https://hpc-wiki.info/hpc/OpenMP is an intro to another one, called OpenMP. Note the examples are given in C and Fortran, and both rely heavily on preprocessors/compiler plugins in order to generate the right code.

Yes, Fortran is still in heavy use, it seems. And if you learned your Fortran before the 1990s (as I did), you may not even recognize it as the same language.