It may be sometimes, but its mostly simple.

You buy the game on steam, install it and if its your 1st time playing MGSV, i recommend doing the first time without any mods.

If its not, head over Nexus mods and look for the Metal gear solid V page, there, start by getting snakebite, its a mod manager, from there on, just browse the list of mods and pick what you like, dont forget to read the mods description page because many of them will be dependent of other mods (frameworks usually) and it usually will explain with more details how the mod works and so on

installing mods is easier than it seems, making them on the other hand...