Managing Twitter means several things.

Regarding content, the person finds appropriate things to post on Twitter, which we do about 4 times a day. This includes both InIn and non-InIn materials that we curate for our audience, and most of the things we post are not InIn content - about 2/3. The latter involves reading the article and determining whether our audience would find it appropriate. Then, the person writes up Tweets with appropriate hashtags for each piece. They put it into a spreadsheet. Then it gets read over by two other people for grammar/spelling/fit. Then, these are scheduled through Hootsuite, a social media scheduling app.

Regarding managing Twitter itself, this involves managing the Twitter audience of the channel, including questions, comments, etc. (we have over 10K followers on Twitter). It also involves reTweeting interesting Tweets, and other Twitter-oriented activities.

This takes place for a number of social media channels. Here's an example of a weekly social media plan for Hootsuite, if you're curious. This includes Twitter, FB, LinkedIn, and Google+.

This doesn't include Pinterest, Instagram, StumbleUpon, or Delicious, since Hootsuite doesn't handle those.