[Doc]Add docs for siem app (#39030)

* Add docs for siem app

* Incorporate more review comments

* Fix punctuation

docs/index.asciidoc

@@ -54,6 +54,8 @@ include::apm/index.asciidoc[]
 
 include::uptime/index.asciidoc[]
 
+include::siem/index.asciidoc[]
+
 include::graph/index.asciidoc[]
 
 include::dev-tools.asciidoc[]

docs/siem/index.asciidoc

@@ -0,0 +1,54 @@
+[role="xpack"]
+[[xpack-siem]]
+= SIEM
+
+[partintro]
+--
+coming[7.2]
+
+beta[]
+
+The SIEM app in Kibana provides an interactive workspace for security teams to
+triage events and perform initial investigations. It enables analysis of
+host-related and network-related security events as part of alert investigations
+or interactive threat hunting.
+
+
+[role="screenshot"]
+image::siem/images/overview-ui.png[SIEM Overview in Kibana]
+
+
+[float]
+== Add data
+
+Kibana provides step-by-step instructions to help you add data. The
+{siem-guide}[SIEM Guide] is a good source for more
+detailed information and instructions.
+
+[float]
+=== {Beats} 
+
+https://www.elastic.co/products/beats/auditbeat[{auditbeat}],
+https://www.elastic.co/products/beats/filebeat[{filebeat}],
+https://www.elastic.co/products/beats/winlogbeat[{winlogbeat}], and
+https://www.elastic.co/products/beats/packetbeat[{packetbeat}]
+send security events and other data to Elasticsearch.
+
+The default index patterns for SIEM events are `auditbeat-*`, `winlogbeat-*`,
+`filebeat-*`, and `packetbeat-*``. You can change the default index patterns in
+*Kibana > Management > Advanced Settings > siem:defaultIndex*.
+
+[float]
+=== Elastic Common Schema (ECS) for normalizing data
+
+The {ecs-ref}[Elastic Common Schema (ECS)] defines a common set of fields to be
+used for storing event data in Elasticsearch. ECS helps users normalize their
+event data to better analyze, visualize, and correlate the data represented in
+their events.
+
+SIEM can ingest and normalize events from ECS-compatible data sources.
+
+--
+
+
+include::siem-ui.asciidoc[]

docs/siem/siem-ui.asciidoc

@@ -0,0 +1,73 @@
+[role="xpack"]
+[[siem-ui]]
+== Using the SIEM UI
+
+The SIEM app is a highly interactive workspace for security analysts. It is
+designed to be discoverable, clickable, draggable and droppable, expandable and
+collapsible, resizable, moveable, and so forth. You start with an overview. Then
+you can use the interactive UI to drill down into areas of interest.
+
+[float]
+[[hosts-ui]]
+=== Hosts
+
+The Hosts view provides key metrics regarding host-related security events, and
+data tables and widgets that let you interact with the Timeline Event Viewer.
+You can drill down for deeper insights, and drag and drop items of interest from
+the Hosts view tables to Timeline for further investigation.
+
+[role="screenshot"]
+image::siem/images/hosts-ui.png[]
+
+
+[float]
+[[network-ui]]
+=== Network
+
+The Network view provides key network activity metrics, facilitates
+investigation time enrichment, and provides network event tables that enable
+interaction with the Timeline. You can drill down for deeper insights, and drag
+and drop items of interest from the Network view to Timeline for further
+investigation.
+
+[role="screenshot"]
+image::siem/images/network-ui.png[]
+
+[float]
+[[timelines-ui]]
+=== Timeline
+
+Timeline is your workspace for threat hunting and alert investigations. 
+
+[role="screenshot"]
+image::siem/images/timeline-ui.png[SIEM Timeline]
+
+You can drag objects of interest into the Timeline Event Viewer to create
+exactly the query filter you need. You can drag items from table widgets within
+Hosts and Network pages, or even from within Timeline itself.
+
+A timeline is responsive and persists as you move through the SIEM app
+collecting data. 
+
+See the {siem-guide}[SIEM Guide] for more details on data sources and an
+overview of UI elements and capabilities.
+
+[float]
+[[sample-workflow]]
+=== Sample workflow
+
+An analyst notices a suspicious user ID that warrants further investigation, and
+clicks a url that links to the SIEM app. 
+
+The analyst uses the tables, widgets, and filtering and search capabilities in
+the SIEM app to get to the bottom of the alert. The analyst can drag items of
+interest to the timeline for further analysis.
+
+Within the timeline, the analyst can investigate further--drilling down,
+searching, and filtering--and add notes and pin items of interest. 
+
+The analyst can name the timeline, write summary notes, and share it with others
+if appropriate.
+
+
+