What is a dream guide and how do you access him/her/it?

[Jenos]

When I say Dream guide i mean the... well, entities that you encounter in your dreams that guide you, not the guides here on the site. I've done a lot of searching (both Google and the forums, even the lucid dreaming subreddit) but I can't seem to find a detailed answer. All I know about these "dream guides" is that they're re-occurring characters in your dream that are present throughout it. So what I want to know is, what exactly is it, and what does it do? And obviously how do I find it when I finally do get successful lucid dreams?