If you have just installed the eSS agent, look up in your system tray to find it. For now, it will be the old eSS logo so it will look something like this if you are on a Mac.
Click on the icon to see the options in the drop down menu, click “Activate” to authorize the agent. Log in using the same credentials you use to log in to eSecureSend in the browser. And so on, etc.
You are now ready to go back to the browser to send the large file.