A quick overview/explanation of Reddit and how it works:
The main reddit page is a list of all the highest voted things of the day. Basically, people can post an item on different "sub reddits", which is a smaller section of reddit that is specifically for one subject. So for example you can have reddit.com/r/gaming which is huge, or you can have stuff like reddit.com/r/shenmue.
After creating an account (for free) anyone can go to these reddits and submit an item. This can be anything from a line of text (like a question or something) to a video, a link to a website, an image, or pretty much anything.
As a visitor to the site, you can Upvote or Downvote the content that people have posted by clicking the up and down arrow on the left side of the page, next to the title name. Reddit when then take into account the upvote to downvote ratio and will display this item on the Sub reddit that it is in.
So for example, I've posted some thoughts on the Shenmue Sub-reddit, (http://www.reddit.com/r/Shenmue/comments/3a75z1/shenmue_3_kickstarter_45_million_is_not_the_end/). If you look on the top right of the screen you can see that it has 24 points, with 95% upvotes. If that is a higher than the other items on the sub-reddit, it will be higher on the page, and will stay around for longer.
Another thing to mention, is that you can comment on any of the items with your thoughts (a lot of discussion goes on here) and people can also upvote or downvote your comments.
I hope that helps, if you need more help let me know and ill be happy to help out :)