From Desert Operations Wiki
Once you've learnt about the Playing Field and its principal components, then I'll tell you about what buildings you should build and in what order you can do it.
Click the white blinking box at your Base and you'll read a suggestion about the next building you should do. Once you have clicked there, an advanced menu will open. Click the Build button. There you'll find how much does the building cost and the time it will take to finish. Below the image representation of your building, you'll see a brief description of it.
In your main screen, in the map, you'll see a small icon and a progress bar telling you how much time is left for the building progress to end. To the right you'll see the total time needed for the construction. In the beginning, your first building will be finished very fast but as you progress in the game, construction times will be longer. To speed up that process, you may use diamonds to pay your workers and they'll do the impossible to finish it early. Diamonds can be purchased by the player with real money, they may be won under certain game conditions or missions and/or by recruiting friends as new players.
When your first building is finished, two things will happen: you'll get your first points and your first achievement. Now click in the next blinking white box. You'll be suggested to build Factories. Keep in mind that these are very important buildings because they'll produce money for the game and sooner than later you'll be building them in large quantities. Next you may type in the text box how many factories you wish to build and, logically, the more buildings you enter, their price and the time spent building them will be longer. When you finish playing around, just click build and let it start. This time it will time more time to finish, meanwhile you may play around to keep learning about the game. Say hello in the chat or something. When you click the factory again in a near future, then you'll see you can reduce the building time and how many buildings of that type you have already.
In the building tree diagram, you'll find the prerequisites to have them all. In the beginning, the rookie (or newbie) protection will be activated and you can't be attacked. Use that time to your benefit to find your optimum build. The protection will be lifted when you reach the 13.800 points. If you attack other player before reaching this score, you'll also lose the newbie protection. If you wish to know which requisites you need to build certain Units, you may find information about this in the University as soon as you've built it.
Tutorial and missions
After some updates, we programmed some missions for new accounts. This missions will help you build your base in a specific order to understand the game better. It's very important that you finish this missions as soon as possible, because some of them can only be done at some levels. For example, the soldier mission should be finished before you reach level 10 in your command center or then it won't be possible to do it. If you don't finish these missions appropiately in their time, you may have problems with the tutorial afterwards.
In some cases, the game will block you from building anything else until you finish a specific tutorial mission (build 3 factories, for example). The system does this to guarantee that you're following the tutorial correctly and you're getting the best advantage from it. If you prefer you can also skip the tutorial and decide on your own what to buld and research.