No worries maz..
You sit in the seat, with your feet down (most people can either get both feet flat down, or at least on the toes).
Put on foot on the pedal (most use SPDs or similar) and clip in if applicable.
Get pedal to good position - which is similar to on an upright - just in front of top dead centre.
Push on pedal, lifting other foot to other pedal.
As with an upright, the momentum of the first push should carry you along until you have both feet on pedals and are turning.
For beginners, the problem is adjusting to the different body position, and balance. As with uprights, some people take to it instantly, some take a few goes, some more. It can help to have someone hold the bike up, allowing you to get both feet up to start. It also helps if you force yourself to push off and lift the other foot gently, in a flowing motion, as opposed to a panicky movement, if you see what I mean. It can make a difference if you are have under- or over-seat steering, but again, people differ - often they falter because they aren't used to the steering, rather than not used to the pedaling position. And some bikes are just inherently more stable, just like the geometry on uprights. Finally, it's also a mental thing. A very few poeple are so determined to fail, or so nervous, that they can't relax into it.
Also of course, the bike has to fit right - you need to be able to reach the pedals properly, and for me, I like to be able to get both feet flat to the ground to feel stable starting off - some seats are too high for my stumpy legs. I was chuffed to sit on the new ICE bike at the CTC rally, and find that it was low enough. Now I just need the money, and a bigger hallway...