What is intimacy?

I have been reading a few articles on the topic of intimacy and am finding it an intriguing topic to think about.
Not so much intimacy when it comes to a one on one relationship like marriage, but it's all about knowing and being comfortable with yourself and others.
That's something I'm not sure about. One of the questions posed in the article was: do you like yourself?
Now the obvious answer is yes, but when I think deeper about it I wonder about how much I do. I'm not always nice to myself, I have bad habits, I'm far too self-deprecating, I worry too much, I could go on.
Are these actions of someone who likes themself? Would I be like that to my best friend? Aside from the occasional disagreement and an hour or two of silence, absolutely not. Why is it then good enough to treat myself by different standards?
Now the article is about growing comfortable with intimacy, things like physical (non-sexual) contact with others, letting other people into your world, communication. I'd maybe scrape a pass mark on the first, fail miserably at the second and for someone who works in that industry my communication skills are ordinary when it comes to personal stuff.
It's not that I don't want to participate, I want to feel closeness that is reciprocated and not punished, like I get now and then. I know we are all a work in progress on a lot of issues. I guess this is one of mine. While I fully understand the concept and largely how it works (I try very hard with certain people but they don't seem to want to play ball and that can be disheartening) it seems like something that takes time to learn, because it doesn't seem to come naturally.