Finally you need to upload this file to Google Calendar.
1. Open Google Calendar.
2. Before uploading I suggest you turn off the notifications (otherwise you will get an e-mail and pop up reminder before every lesson). Go to settings (the grey cog on the top right), then Settings, then calendar on the top menu bar. Finally select your calendar (usually your name) and go to Reminders and Notifications and turn off Event Notifications.
3. Back in your calendar - there is a little drop down arrow next to Other Calendars - press this.
4. Then select Import Calendar and then import the file you downloaded - it may take some time - but will upload your timetable into Google Calendar.