|Dirt blocks 2 metres apart.|
First place some dirt/grass blocks two spaces away from each other.
|Torches on the sides|
To speed up the growing, or if you are growing indoors place torches on each sides of the dirt.
|Saplings on top.|
Place a sapling on top of each dirt block.
Wait a couple of Minecraft days.
(Don't worry if your trees all don't grow at once, it's random.)