Grafana is the visualisation layer. It connects to data sources (Prometheus, Loki, CloudWatch, Elasticsearch, etc.) and renders dashboards. Grafana itself doesn't store time-series data — it queries other systems.
Key Grafana concepts: dashboards (collections of panels), variables (templating to make dashboards dynamic), alerts (Grafana can also fire alerts based on queries), data sources (Prometheus, Loki, CloudWatch, etc.).