What are instances and how do i make one?

Instances are the atomic things that make up the ROBLOX environment. Each one takes up exactly one line in the explorer.

Instances on Wiki

Here are some examples (lists are incomplete):

Parts (Part, SpawnLocation, WedgePart, TrussPart), GUIs (TextLabel, TextBox, ImageLabel, BillboardGui, ScreenGui), Meshes (SpecialMesh, CylinderMesh, BlockMesh), Effects (Fire, Smoke, Sparkles, ForceField, Decal, Texture), Containers (Model), Tools (Tool, HopperBin)...

Instances are primarily made with the function

Instance.new( instancename , parent ).

Here, instancename is a string corresponding to the ClassName of an instance (also the title of its Wiki article, and its entry in the Object Browser).

You can also get a new instance using the Clone method on any existing instance, which will make a copy of it and all of its children.

Instances are everything you see in the explorer. Basically everything. You can create one by doing Instance.new("Instance name",parent)