The core of Prometheus is an timeseries database with a powerful query language. Prometheus also support alert management with a separate tool, alartmanager.
Prometheus is is built for the cloud and have support for different kinds of discovery functions to support changing and elastic infrastructure.
Prometheus is simple, yet powerful, but it do not try to cover every aspect of the observability space, like long term storage of metrics data.
The architecture is poll based and collecting metrics is done using proxy “exporters” that immediate between infrastructure and application specific metrics to prometheus metrics format.
Together with Grafana, Prometheus is a powerful solution for metrics aggregation, alerting and visualization.