Since each mod usually comes with its own installation instructions, I am going to focus on frameworks and libraries that most mods utilize along with Mod Managers. If you are caught modding GTA V Online, it is considered cheating and you'll likely get banned unless if you know what you're doing. Therefore, please only use these mods in singleplayer. While GTA V mods are allowed in singleplayer, they are not allowed in GTA V Online. Mods can range from allowing you to fly/run incredibly fast to improving the game quality itself via better models, textures, or code.
GTA V mods are community-made modifications that allow you to alter gameplay. Modding is extremely powerful in Grand Theft Auto V (5) and gaming in general.