You may like to look at my tutorials for pursuit algorithms here https://sparse-plex.readthedocs.io/en/latest/book/pursuit/omp/algorithm.html .
I build the discussion step by step from basic ideas for pursuit algorithms, moving on to matching pursuit and then delving into OMP.
There is a hands-on section on OMP which guides through the execution of OMP on a simple problem step by step https://sparse-plex.readthedocs.io/en/latest/book/pursuit/omp/algorithm.html#hands-on-with-orthogonal-matching-pursuit.
I also provide an extremely fast implementation of OMP which is discussed here https://sparse-plex.readthedocs.io/en/latest/book/pursuit/omp/fast_omp.html