Reddit is a somewhat cleaner 4chan. That's good. It has a lot of stuff for everyone, from religion to politics to hacking to building stuff to conspiracy theories. I'd say that it is the front page of the internet ;).
It is a good, trustworthy site, don't get me wrong. You are at extremely low risk of harming your computer as long as you aren't clicking malicious links (moderator quality does depend on the subreddit, but overall they're pretty good for keeping malicious links off the site). However, the community is not the most egalitarian; it's all about your karma, registration date, and whether you go with the group mind. Be prepared to be relentlessly downvoted or have your posts deleted if you go against the groupthink of your particular subreddit.
Reddit is a great way to find stuff from all over the internet, but in my experience, I prefer lurking and reading links as opposed to being an active member.
PS: I do not use this username on Reddit, so don't go downvoting my comment on here if some other nerd with a similar screename made you angry.
Reddit is a site where users can post links to, comment on, or discuss nearly any kind of content or subject. Each subforum, or "subreddit" has its own rules, subjects, and moderators. Some subreddits are fine for kids, others are for adult only, most fall some where in between.