The commands you use most are on the Ribbon and readily available all the time. Some other commands appear only when you may need them, in response to an action you take.
For example, if you don't have a picture in your Word document, the commands to work with a picture aren't necessary.
But after you insert a picture in Word, the Picture Tools appear, along with the Format tab that contains the commands you need to work with the picture. When you are through working with the picture, the Picture Tools go away.
If you want to work on the picture again, just click it, and the tab appears again, with all the commands you need. Word knows what you are doing and provides you with the tools you need. The Ribbon responds to your action.
So don't worry if you don't see all the commands you need at all times. Take the first steps. Then the commands you need will be at hand.
You'll see how this works in the practice steps at the end of the lesson.