Friendless, gay virgin here inquiring about what sex is like. Is intercourse painful? For both giving and receiving. I don't watch porn, I only jack off to still images of fully clothed men.
		
		
	 
First, don't be ashamed to be curious about 
unclothed men too.  Arousal and erotic curiosity are all natural parts of the human experience.  Unless you know the images were taken without consent of the person shown, it is not unethical to look at naked men.  You are not cheating on your future boyfriend by looking at naked pictures.  And it will help you to understand how all men are different in their anatomy.  This is a practical thing to know for anal sex.
Second, no it is not painful. Whether you're giving or receiving you should never feel anything that feels like pain, burning, tearing, or scraping; that means you should stop, take a break, reposition, talk to each other about what might feel more comfortable and what would be a sexier position instead of an uncomfortable position. If you're inside your guy and he says "I think I need to try this lying on my stomach instead," then that's what happens right away.  
Receiving - it will feel weird at first because it is a unique sensation that your body has to figure out. But "feeling weird" is definitely not 
pain. With my guy, we stopped plenty of times until we learned how to do it comfortably.  And it is a skill that requires learning.  So even if the first moment together in bed is thrilling and unforgettable, don't assume the first time will be as good as the 10th time. It's a fun thing to practice.
Please don't think it is about tolerating or inflicting pain. It just isn't.  For my guy and me, intercourse is only about the pleasure we can give each other, not how much we are willing to endure for each other.  Now that I know more about my own anatomy and his, we can get right to the pleasure.
A couple of other things. Even though I've been with my guy for years and we have things figured out, there are still times where it randomly could feel uncomfortable for one or both of us.  Things back there sometimes have a mind of their own, and even if you're horny, there is no guarantee your ass will be.  That's fine, there is other fun stuff to do in the bedroom.
Also, obviously there are some times which are not appropriate for anal sex.  If you feel like you might have to go to the bathroom soon, it's not a good time.   
That's pretty much the basics.  Buy a good-quality lube from a pharmacy, don't try to improvise or use suntan lotion or something.  Go to the pharmacy and buy proper lube for sex.  Try a couple of different brands.  And actually learn what things feel like back there with a reasonable sized sex toy or even your fingers if your nails are short and smooth.  It's not wrong or weird. It is just knowledge in the pursuit of pleasure, for you, and the guy who you want in your life.