explorer220-start query (#1085)

docs-2.0/nebula-explorer/ex-ug-query-exploration.md

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+# Start querying
+
+!!! note
+
+    Select and click a target graph space before querying data. 
+
+!!! compatibility "Legacy version compatibility"
+
+    For versions of Nebula Graph below 3.0.0, you need to create an index before querying data. For more information, see [Create an index](../../3.ngql-guide/14.native-index-statements/1.create-native-index.md).
+
+Click the **Start** ![query](figs/nav-query2.png) icon to query target data. The queried data will be displayed on the canvas. You have the following ways to query data:
+
+- Query by VID
+- Query by Tag
+- Query Subgraph
+
+## Query by VID
+
+You can enter VIDs to query the target vertices and then start data exploration and analysis based on the vertices.
+
+There are three ways to generate VIDs: Manual input, Random import, and File import.
+
+!!! note
+
+    - The VIDs entered or imported must exist in the graph space you have selected. 
+    - Only one VID per row is supported in the querying area.
+
+The following GIF shows how to query data using the `nba` graph space and related data.
+
+![VID QUERY](figs/vid_query.gif)
+
+## Query by Tag
+
+!!! note
+
+Make sure that the corresponding tags and indexes exist in the graph space when querying by tag. For more information, [Create tags](../3.ngql-guide/10.tag-statements/1.create-tag.md) and [Create indexes](../3.ngql-guide/14.native-index-statements/1.create-native-index.md).
+
+You can limit the number of results and filter the results.
+
+The following example queries 10 players whose age is greater than 30 years old and not equal to 40 years old.
+
+![tag](figs/query_tag.png)
+
+## Query Subgraph
+
+When querying subgraphs, you must enter one or more VIDs. You can specify the number of steps, edge types, and the direction of inflow and outflow of the subgraph. 
+
+The following is an example of VIDs `Kings` and `Suns`, step number `2`, and incoming edge types with a VID value of 101, the number of steps of 4, and edge types of `server` and `like`.
+
+!!! note
+
+    When multiple VIDs are entered, the VIDs are separated by the Enter key.
+
+![tag](figs/query_subgraph.png)
+