StarCraft/Tutorial: Boot Camp
Before the campaign actually gets under way the game provides an optional tutorial at the beginning of the Terran campaign. The requirements of the tutorial are quite simple and designed to simply get you familiar with the basics of unit movement, resource gathering, and construction. The objectives read: Construct 3 Supply Depots and Construct a Barracks. When the game starts you will notice that you have a small number of SCVs and sixteen marines. Get to work immediately gathering the provided minerals with the SCVs and begin construction of a few more. Continue putting the SCVs to work mining as they appear. Before advancing onto the next level, definitely practice coordinating efforts as efficiently as possible; you will learn much about economy management by doing so.
It is very difficult to lose the tutorial and you will never have to face an enemy attack. You should practice rotating marines to avoid losing any HP; you should be able to consistently defeat all of the Zerglings without getting a single Marine injured.
As you get past 100 minerals pull one of the SCVs off of mining in the mineral field and send it over to begin building a supply depot. You can build it anywhere around your base although to avoid clutter it is recommended you try to build it away from your SCVs working. In order to construct a supply depot select your SCV and click on the basic build button at the bottom of the command selection screen in the bottom right corner. The Supply depot will then appear in gold in that same window for you to select and place. Two more Supply Depots will be required before you will fulfill that requirement. After you have the supply depots wait for 150 minerals and construct the barracks in a similar manner wherever you like. Once the Barracks are completed you will be greeted with the mission completed screen.