When you go to the dashboard, you can click on the download ActivTrak agent for Chrome and you will be taken to the download page on the Google App Store.
Additionally, you will need to go to Account>ChromeBook Users and invite users with the email addresses they associate with Chrome. This ensures that the data goes to the correct account.
The user will get an invite they will need to accept, as pictured below.
Please keep in mind that they will need to be logged into the Chrome Browser in order for the agent to work properly.