2 Answers. According to Wikipedia: Users gain one point of link karma when another user votes up their submission and lose a point when a user votes down their submission. Individual comments may also be voted up or down by other users and result in a user's comment karma.
You should have 30 to 40 karma points to post in subreddits. But some subreddits like r/branding are open for the users having 610 karmas.