You learned two SCC algorithms: Kosaraju (two DFS passes with graph transpose) and Tarjan (single DFS pass with low-link values). You saw how to build the condensation graph and use it for DP. You solved three CSES problems: Planets and Kingdoms (detect SCCs), Coin Collector (SCC + DP on DAG), and Flight Routes Check (strong connectivity test).
SCCs compress directed graphs with cycles into DAGs. Use them when you need to simplify graph structure, find mutually reachable groups, or detect circular dependencies.