What's a Reality Check?

I don't really get what a reality check does. I'm new to this Lucid Dreaming. I Don't even know how to do it. I want to do MILD, help, Thanks :)

A Reality Check is something you try to do, what's only possible in a dream. E.g. trying to breathe through a pinched nose, leaning against a wall to look if you fall throug, trying to push your thumb through your palm etc. I'm kinda a newby too, but I have had one succesful Lucid since I started using reality checks (have had some lucids before, but I didn't really care and didn't really know what they were...).

A reality check, or RC, as used on this forum, is a test used to determine whether or not you are dreaming. A common example is plugging your nose and trying to breathe through it. In waking life, this would be impossible, but in a dream, you can breathe just fine. There are many different kinds so there is one for everyone. That is just the most common.

It is exactly as it sounds. You check whether you are dreaming or not. Read a tutorial in tutorials section.