once youìve installed LME4 as explained by Iutland, the big part of your hard job is done. To use Pdgurian units you must ONLY 1.out the pack file of his units into data folder and then open LME4 launcher, click on "manually edit user script" and add the names of the pack at the edge of the list for example,: mod "Pdguru_Coalition_Minimod_2-2.pack";
hope it will help you!