As you run your grand empire in Empires and Allies, you'll find that there are a variety of actions that you must take in order to keep your empire up and running. Some actions are easy, like collecting money from a small hut or clearing land, but other require a bit more effort (You are running an empire after all).
That's where Empires and Allies energy comes in. Empires and Allies energy becomes important when you want to finish a building, or even have your units attack in battle. So, naturally, you're going to need as much energy as possible to maintain your glorious empire.
Thankfully, there are multiple ways to obtain energy. Energy is valuable, so it's not going to just appear out of nowhere, right? Wrong. The most basic way to obtain energy in Empires and Allies is to wait, because your energy replenishes over time. Mighty emperors don't have all the time in the world, however, and that's why there are other ways to gain energy.
One major way is to socialize. The more friends you get to play with you, the more energy you can send to them for free--and the more energy you send to your friends, the more energy they are likely to send back to you. And that's not all. Remember when I mentioned that your units require energy in battle? Well it just so happens that winning in-game battles is yet another great way to get energy. The spoils of war are plentiful!
Now that you know how to get energy, you can start playing and racking up as much energy as possible by pulverizing your enemies and gathering your allies. The best part is that it's fun while you do it!