Once your seedlings have germinated and are ready to move on, it's time to prick them out.
Gardeners have different preferences as to when to do this - normally you would wait until they have their first set of 'true' leaves ie not their first 'seed leaves' which are the first two that you'll see, but the set after that.
However if you have hundreds of tiny Ammi or Poppy seeds for example growing like cress in your seed trays and they are starting to get leggy, you can do it, if you're super-careful and have fingers like a fairy when they're just a couple of centimetres high.
Here's how!