Mimir exposes both remote write API and Prometheus compatible API. The typical setup is that you configure Prometheus (or Grafana Agent) to remote write to Mimir and then you configure Grafana (or your preferred query tool) to query metrics from Mimir.
You may also be interested into looking at a 5 minutes introduction video, where I cover the overall architecture too: https://www.youtube.com/watch?v=ej9y3KILV8g