Nesting is one of the most important features of the game. If you go into bins, or if you happen to find a twig from the orange arrow on your compass, then chances are you have found a twig. After you have found a twig, fly to a spot of your choice and press the space bar; there, you have started your nest! But be careful, sometimes if you start a nest on a tree it will not accept it, as you were not placed exactly on the branch. So, to avoid losing your twig, avoid building on trees or in mid-air. Also, if you already have a nest and try starting another one somewhere else, you will lose the twig. You can also find twigs lying around in random spots on the playing field. You can find your nest again by using your compass/radar on the upper-left corner of you screen. Follow the ORANGE arrow on your Radar to find twigs, and the PURPLE arrow to find your nest location.
Once you have created a nest, visit it about four to five times with twigs, and then you can lay an egg. You can also use your eggs as bombs to drop on other players like poo, although it takes up a lot of the poo-o-meter. A new egg will be available to use once you add another twig to your nest, even though it is already completed. After a while, you will have to add another twig to your nest, even though it is already complete to have an opportunity to lay an egg again. Be sure to be in the very centre of the nest, otherwise you the egg will be wasted. Then, after laying it, you have to incubate it for a while to prevent it from cooling down.
Once the egg hatches, you will have to feed your chick, but not that often. This allows you to fly around searching for food, which you will then have to share with the chick. You will have to feed the chick many times, and after a while a message will arrive in the top right-hand corner saying: "Your chick has grown up!". Visit the nest one last time to see your chick as a fully grown bird which will then fly away from where your nest was at.. Another message will then appear: "One (your bird species) successfully reared by (username)!". Afterwards, you will then receive an extra life.
You can also add the twigs you find to another player's nest. This can be a form of kindness, but if repeated you will become some sort of mate for the nest's player. If the player agrees, you can help warm the egg and feed the chick once it hatches (you have to be the same bird species in order to feed their chick). Of course, there are the kind of players that go: "I will help your nest and you will like it!".
It is also possible to break another player's egg or nest, but it is hard to tell how. When you leave the nest alone for some time, a rustling sound can be heard. It is the same sound that you hear when a twig is added to a nest and when you find a twig. That rustling sound is also heard when your nest shrinks. Your nest can shrink to the point where it disappears or breaks. To remedy that, add more twigs! If your nest does disappear, you will receive a message saying: "Your nest is broken!" in the top right corner of the screen, and you will have to find another twig to start the whole nest building process again.
If you want to build a nest in peace without getting pooed on by other birds, play in singleplayer or go into an empty room in multiplayer.