By now everyone has heard of Twitter and tweets. Twitter is a free micro-blogging platform in which tweets are limited to 144 characters. That is mighty concise.
Sign up at Twitter for a free account. Create a simple profile that tells people who you are. If you don't have a picture you want to use, or are shy, use a baby picture, simple icon or avatar. Then tweet something simple. Web links are great, but use a URL shortener like bit.ly or goo.gl so you stay within the 144 character limit. You can also upload photos. Don't have any subscribers yet? You will.
Meanwhile, I recommend that you check out Welcome to Twitter. It is a great resource and a perfect place to start.
If your students are old enough to have accounts, then they can subscribe to your twitter feed (that is what it is called). Because tweets are short, they are well suited for short attentions spans. Students can access Twitter on their smart phones as well as on computers. It is a great way to instantly poll students. Students can use it as a backchannel in discussions.
Teachers who already have personal accounts typically create separate accounts dedicated to the class(es) they teach. For example, I created @rickeducation. If you wanted to email me at Twitter, you would send it to https://twitter.com/rickeducation.
Twitter has become a go-to pace for asking important questions to which you need relatively quick answers. Read the article, Twitter hashtags every teacher ought to know. It will show you how to instantly connect to a host of communities indicated by hashtags. For example, I often include #edchat in my tweets to join a bunch of other educators. I use #CCSS when it is related to Common Core.
If I want to cite a specific author, I use the @ symbol. For example, if I tweeted about a great article in the MindShift blog (which I highly recommend), then I would include @MindShiftKQED in my tweet. All of this of course in 144 characters.