Terminology

Some basic explainers for some of the terms used. 

Client Side / Server Side 

Client Side is whatever the player installs on their computer - some mods like font replacers are usually client side only, meaning only you would see the changes. Server Side mods usually need to be installed on both Server and Clients. Sites like Modrinth will say whether a mod is intended for Servers or Clients.

Mods

Anything that modifies the game from its vanilla state that is more complex than texture or audio swaps. Mods can be as simple as adding new block types (like furniture or new ores) and as complex as adding realistic physics to the game or porting the entirety of the Pokemon series and its game mechanics. 

Modpack

a Modpack is a zip containing the mods as well as info about which version of Minecraft and Mod Loader to install. Installed via drag and drop with a launcher like Prism Launcher. Modpacks are a curated collection of mods intended to be used together, and contain all necessary dependencies needed to play. 

Resource Pack

Resource Packs allow changes to textures, models, music & sounds, splash screens, fonts, etc without any code modification. Resource Packs are also in .zip format and installed via drag and drop, or installed directly through a launcher. Previously referred to as texture packs, renamed when more asset types became supported. 

Shader Pack

Shader Packs are mods that enhance the visuals of the game. They can add things like volumetric clouds, waves and caustics in the water, bloomy lighting, ray traced lighting effects, and more. Shader packs are client side so every player might have a completely different visual experience within the same server. Some shaders are more like a vanilla+ experience, while some make it feel like totally different game. 

There's a range of options available for shaders, from cartoonish or fantasy, to hyper realism, and some are specifically tuned for low-end computers with onboard graphics. Some example shaders to check out: Aurora Fantasy, Complementary-Unbound, Complementary-Reimagined, Rethinking Voxels, Solas Shader, BSL Shaders, and Sildur's Vibrant Shaders.