OSPF: the same map for everyone, each with its own path
Every mechanism has a step-by-step animation, the configuration explained line by line and the exam notes. Where a parameter changes the outcome, you get a simulator in which you change it yourself.
TL;DR
OSPF is a link-state protocol: routers describe their links in LSAs, flood them reliably across the area and all end up with the same database, on which each one runs SPF. Adjacencies go through well-defined states, from Down to Full, and on broadcast segments a DR coordinates the exchange. Areas limit the detail: ABRs advertise only prefixes and costs between areas, ASBRs bring in external routes (E1, E2), and the special area types filter them. On top of this core: summarization at the borders, authentication, OSPFv3, fast convergence and integration with provider networks.
How to read the notes: red = critical for the exam, green = theory, blue = numbers, yellow = pitfalls, cyan = RFC ↔ Cisco differences. In the animations, the configuration lines used at the current step are highlighted automatically; the ← → arrows change the step while the animation is selected.
The analogy, in short
Think of a city with sectors. Every control center (router) has the same map of its sector (LSDB) and computes its own routes with its GPS (SPF). The sectors (areas) send each other only summaries, through the border intersections (ABR), and all travel between sectors goes through the central ring road (area 0).
The model holds up to §10. From §11 on (OSPFv3, fast convergence, PE-CE), it breaks; see the full analogy and its limits in §16.