To properly install the Azure DevOps Plugin, make sure to complete all three steps, as detailed in this article:

Step 1: Installing

Open the CloudShell Colony Plugin page in the Azure DevOps (VSTS) Marketplace.
Click Get it free.
Log in to VisualStudio.com and select the organization that will use this plugin.
Click Install.

NOTE: If you are not the organization’s admin, you may send a request to the admin to install the plugin for you.

Your plugin is now installed.

Step 2: Configuring the Azure DevOps (VSTS) Plugin

Open your VisualStudio.com project.
1. Open the Project Settings/Services page.
2. Click New service connection and select CloudShell Colony.
3. To the Connection Name, enter "Colony."
In CloudShell Colony, open the Settings page and click Integrations.
1. Under the Azure DevOps icon click Connect Now.
2. Copy the automatically generated token.
3. Switch back to Azure DevOps Web UI and paste the token into this field.
  
  NOTE: The token value is generated by CloudShell Colony.
4. Click Verify connection and make sure the connection succeeds.

To start launching sandboxes from your Azure DevOps pipeline, see Launching a Sandbox from Azure DevOps (VSTS).