Fallout 4 is a great game, and the modding community is just as great. Mods have greatly improved what Bethesda has overlooked or didn't bother to add the original game. The best part of modding is modders are always around. There are many types of mods, ranging from new weapons to item retextures. Some make the game much more crazy and others make you delve more into the universe, not to mention how much lore Bethesda added on their own.
Nexus is a great place to get your mods. Combined with Nexus Mod Manager (NMM) is a great way to sort and download mods for Fallout and many more games.