Three things that cleared up OSPF for me:

1. Hellos live on the interface

You run show ip ospf interface and you see timers per link. You break one link and you drop that adjacency. Hellos belong to the interface, not the router.

2. Passive-interface keeps hellos where you need them

router ospf 1
 passive-interface default
 no passive-interface Gi0/0

You send hellos out Gi0/0 where a neighbor lives. You suppress hellos on loopbacks and SVIs where no neighbor will answer.

3. Wireshark shows how LSAs move

You filter ospf and watch the exchange: DBD, then LSR, then LSU, then LS Ack. You see the sequence on the wire. The textbook diagram stops feeling abstract.

Next up: multi-area OSPF and when you use it.