First start with your piece of a4 paper lying in portrait view.

Next, fold the top two corners so that they meet in the middle like in the picture above

Now fold your piece of paper in half so that it looks like this

Now fold the top part of the aeroplane so that it will be able to fly strait. You can make them as big as you like

Now do the same for the other side

Now fold the end corner of the 'wings' so that it can go fast

Do the same for the other 'wing'

Now you can write a message inside to someone