backup my calender online

I'm not sure what that means. If you have a local calendar right now, you'd need to create a network calendar to be able to view it from other machines than your local computer.

Thanks for your help! I would like to have the calender stored online and be able to view it from any computer eg internet cafe if I am out. Will creating a network calender solve this and if so how do I do this?

Look at, for instance, Google Calendar. Your email provider or your ISP may offer something similar. If it supports caldav, ics or similar, Lightning can probably work with it.

Thanks, but not sure if that is what I need. Is there a way to 'publish' the calender on the web so that I can access it if I am away?

You have it slightly back to front. ;-)

You create a calendar, on the 'net, that Lightning can work with. Therefore it is intrinsically accessible via web browsers and the like. For convenience, on your own computer it can be accessed through Lightning in the context of your mail/news/calendar tool, Thunderbird.

Got it - that will work! Thank you!