Stacking is the word for arranging ships in battle. You are allowed a maximum of 10 stacks, or rows, of ships to do battle with. The stack of ships with the highest power goes on top, followed by the next highest, and so forth. For example, if Ship 1 has a power of 10,000, and Ship 2 has a power of 5,000, and you build one of each, Ship 1 will be on top followed by Ship 2. You can view your stacks once the ships are built by clicking on "Manage Fleet." This page also allows you to disband ships.
Fighting is one of the more difficult aspects of the game because it requires a little bit of experience, combined with luck, good timing, and the ability to anticipate what type of fleet a given opponent will have.
Most importantly for you, building and maintaining ships costs a fair amount of money, and lots of people have gone bankrupt in this game because they weren`t careful about watching their money. So, don`t build more of a fleet than your empire can support. Start small, doing battle with people below 100k for the most part. That will help you get the hang of the basics. As your empire matures, you have the ability to fight at higher powers without worrying about money as much.
If you have any more questions, post them here or send a personal message to a Guide in the game.