When a user tries to submit a link on reddit, he will be asked to enter a category (called a subreddit) relevant to the link content:
The default category is reddit.com. You can get a list of the most popular subreddits from here. You can also organise your favorite subreddits by clicking on the Edit Subscriptions in the My Reddits menu as follows:
You can add and delete entries by clicking on the left hand side +/- frontpage links. For example if you want to select only IT related subreddits:
Make sure you share this article on reddit in the internet subreddit!