Slack

Refer the following steps to create a slack based contact point in Grafana.

Create a slack app and an incoming webhook following these instructions.
Navigate to Contact points tab in the Alerting section of the Grafana instance.
Click on Add contact point, give a name to the contact point and select Slack from the Integration drop down.
Add the webhook created from the first step under the Webhook URL option.
Add the following snippet under the Title option in the Optional Slack settings section:

[{{ .Status | toUpper }}{{ if eq .Status "firing" }}:{{ .Alerts.Firing | len }}{{ end }}] {{ if .CommonLabels.cluster }}[{{ .CommonLabels.cluster }}]{{ end }} {{ .CommonLabels.alertname }}

Add the following snippet under the Text Body option in the Optional Slack settings section:

           {{ with index .Alerts 0 -}}
        :chart_with_upwards_trend: *<{{ .GeneratorURL }}|Graph>*
        {{- if .Annotations.runbook }}   :notebook: *<{{ .Annotations.runbook }}|Runbook>*{{ end }}
      {{ end }}
  *Alert details:*

  {{ range .Alerts -}}
  {{ if .Labels.severity }}>*Severity:* `{{ .Labels.severity }}`{{ end }}
  >*Description:* {{ .Annotations.description }}
  {{ if .Annotations.printDetails }}>
  >*Details:*
  {{ range .Labels.SortedPairs }}>• *{{ .Name }}:* `{{ .Value }}`
  {{ end }}
  {{ end }}
  {{ end }}

While this standard alert template should be sufficient for most use-cases, you can also customize the alert template using the Grafana documentation.