Let's break down what we're about to learn.
Game Engine: The engine of which all things are compiled to make a game run. There are open systems, such as Unreal Engine, or closed systems, such as the Creation Engine for Bethesda games.
Models: also called ‘meshes’ these are the shapes of the items you see in game from characters, npcs, hair, trees, animals, boxes, etc. From this point on all solid objects will be referred to mesh or meshes.
Textures: these are the graphics applied to the meshes
Scripts: tells the game engine how to display the information above (and other stuff!)
Effects: these are misc movement models, such as fireballs, waterfalls, etc, to create the illusion of movement in game, also referred to as “fx”
Sound/Music: Self explanatory, in some cases you will also see the term "Sound FX" or "SFX" as shorthand.
A mesh is a specific item that is displayed in game that has two functions: static or moveable.
A static item is a box or a tree or even a mountain, but a moveable mesh is a character or animal (notably, their skeletons).
In order for meshes to “feel” solid in game they are given what is called a “collision” box. This “box” can be any shape, but the point is to make sure there is a contact with the environment to feel realistic. If you ever wonder why you walk through a person at times it is because the model does not have a collision box, or it is too small. In some video games we hear the term “hit box” which is really just a term for “collision.” Some models require bigger boxes, so the bigger they are, the more area there is to connect with. In Skyrim many meshes also contain “skinned” info which are bone nodes that allow them to flop around and have animations.
Textures are the graphics you see wrapped around the meshes. They show colour, light reflection and more. There are several sub-categories of textures to understand.
Diffuse map: This diffuse map are the bright R/G/B (red green blue) colours you see.
Normal map: this is a map that is hidden under the Diffiuse map; it tells the game where to send shadows. A graphic without a normal map is flat
Mask: A mask defines which surface should be affected by which section of a material. These are either greyscale or a single “channel” such as Red, Green, Blue or Alpha. Masks are used often for character creators to give different skin and hair colours.
Emissive Mask: these are masks used for lights on armour, such as Mass Effect. Think of it like a little glow bug inside the texture paths. Because, really, that is what they do- glow!
Alpha: Alphas are part of textures used to define an area. Say you have a piece of armour but you hate the belt on it. You can open up the texture file and under the alpha properties colour over the area you want to be invisible, save it and in game that belt is “gone.” The model is still there, but not visible to the eye.
Different games uses different scripts, which are lines of code that execute a command. Skyrim, uses Papyrus. The Dragon Age Toolset uses Python. The meatier codes for the engine are generally a variation of those scripts that modders use and C++. Depending on which game you are modding depends on what script you use. There are hundreds of tutorials out there for people to use.
Note: papyrus is dependant on FPS, not the other way around. For a long time people swore that papyrus bogged down FPS but this is simply not possible.
Visual effects are more textures set to animate at specific times. There's really nothing special about them. Depending on the game and which mesh system is used depends on how the texture is animated. For Skyrim we use the Havok system which has animated nodes to display effects.
Sound effects are attached to either the music you overhear at times denoted by the devs, or attached to specific items and/or NPC actors.