While you are leveling and researching and building you will find yourself low on or out of resources. Well there is an answer to this, go out and plunder your enemy. This will slow their progress as they will now be low on resources to build and progress, while help you get ahead and defeat your foes. Everyone goes about this process in different ways, the most common being Teleport to a CZ and scroll around the map find people you wish to deplete on resources. Usually they also look for people who are inactive as they are not using up their resources and they are building up while said player is offline.
An active player will have a Green Diamond next to his/her city name, as shown below. This tells you that said player has been online in the past 2 days.
Finally when a player in inactive for 7 days or more you will see a Red Diamond, as shown below.
When plundering in the same civilization as yours you must be the same Age in Progression as the player you wish to plunder. The only exception to the rule is Castle Age and Empire Age players can plunder each other.
To find plunders anywhere on the map that you can reach is quite easy, you must first click on your Hall (shown in the picture below.
This will take you into your Hall where you can see may things, the picture below will show you the War Room which will make plundering quite easy for anyone.
By clicking on the Hat witht he dagger beside it you will enter the War Room.
In here you will see tabs, you obviously click on the "Plunder" tab. This will list places near you on the map that are available to plunder as well as showing players activity by the Diamonds. You can scroll around on the map shown on the right side of the above picture to go off to plunder someone in a different Civ. You can also save the coordinates so that you may find them easily in the future. And Remember to make your trip shorter you are best off to Transport to a Contested Zone.
There is a very useful way to find out who is the best target to plunder and has the most gold. Go to rankings, player, then scroll down to gold. If a player has 30+ million one plunder can make a long trip well worth it.