The Cloud Shell Editor can be launched in different ways to best fit your use case.
Launch a standalone Cloud Shell Editor session
The easiest way to start a Cloud Shell session and begin using
Cloud Shell Editor is to directly launch a
Cloud Shell Editor session with
ide.cloud.google.com.
You can still access the Cloud Shell terminal at any time by
clicking 
Open terminal in the Cloud Shell menu bar.
To launch a standalone Cloud Shell session with both the Cloud Shell terminal and Cloud Shell Editor automatically started, use shell.cloud.google.com instead.
Launch Cloud Shell Editor from the Google Cloud console
To launch a Cloud Shell session from the Google Cloud console,
click
Activate Cloud Shell in your
Google Cloud console.
This launches a session in the bottom pane of your Google Cloud console.
To launch the editor, click 
Open Editor on the toolbar of the Cloud Shell window.
Launch from the Cloud Shell terminal
From the Cloud Shell terminal (accessible by clicking
Activate Cloud Shell in your
Google Cloud console), you can run
the following command:
cloudshell edit .
This launches the Cloud Shell Editor in the same pane.