There have been some top notch answers to your question, but I would like to add my thoughts about defending against the right hand. My belief is that boxing is all about counter-punching; you are always looking to counter. It is hard to counter off an opponent's jab because he can jab and move. So you want him to throw a right hand because then he sets his feet and is in one place long enough for you to work off of it; plus his weight is moving, so you can time that movement and turn him into a counter punch.
Blocking a right hand is a wasted opportunity, especially because your opponent should only be throwing a right hand because you make him do it. Maybe he really wants to throw it, so you drop your left hand and invite it. maybe he doesn't want to throw it, so you lean into his jab and take it off the top of your head, give him some, to entice him to throw it. But when he throws it, you make him pay for it. And pay for real because he commits weight to the right hand.
Now, I know you are just starting out and are kind of tripping on getting hit so this seems way off in the future to you. But you start training your mind- the way you think about boxing and fighting, etc...-as soon as you start training your body. The most certain way to get rid of the fear of getting hit is to quit worrying about 'defending' and to start thinking about how to make it work for you. Am I making sense? You go from thinking 'damn he hit me' to thinking 'I almost made that move. next time I'll do this..."
You start thinking proactively; what you are going to make him do, how you are going to take advantage. You see everything in the context of what you cause to happen. That is how you fight with that left hand where it should be without feeling vulnerable.
The one thing I can guarantee you is this...If you want to get hit with right hands all day long, keep your left hand real high, so you cannot see the punches coming.