Use a SSH client (e.g. PuTTY, FireFTP, etc)
Give it the device IP address, select SSH, port 22.
These are the default user account details:
Password: [email protected] (this will likely may have been changed by you when ssetting up the device)
If it won't connect try re-booting the device (we had to after it had done an update to get SSH to work)
Windows PowerShell Session
The Power Shell for IoT Core page