A diorama is a scene of a particular moment in time. Typically a diorama is a miniature replica of a scene, in this video Youtube channel CraftStation creates a realisitc diorama of a Merkava tank 1.35 scale where he catches the moment of the tank firing.
This tutorial uses some store bought materials like the tank and miniature figures but it also gives you a lot of great tips on how to improvise materials. Watch the video from CraftStation for more info:
The scale of the diorama is one of the most important decisions you will make and you should decide on this before you purchase anything or start building anything. The larger the scale the better the detail and the larger the diorama.
You can create your own little world of armor and or figure models that can appear as a freeze frame of a historic event or anything else you want to be.