Minecraft Mods are modifications made for your Minecraft adventure, there are paid and free mods made for single player and multiplayer. You will find a wide variety of mods. for example: Decorations, Graphics Improvements, Game Optimization, Adventure, Weapons, Armor and tools that allows you to have any items without having to look for them.
The most recommended mods for you are:
OPTIFINE HD: is a tool that improves the graphics of the game by adding shaders, besides optimizing the game giving great impulse of FPS, and options of ingame configurations for better performance.
MINECRAFT FORGE: is a necessary tool for you that likes to install Minecraft 1.13.1 Mods, it was designed to guarantee to the creators of mod a compatibility between mods of different authors.
MINECRAFT SHADERS: These are shaderpacks that work together with Optifine and allow you to have very beautiful graphics, with lighting, reflections and high quality shade (For Advanced Players).