I have always wanted to be a journalist, which is a person who writes news or other current information to the public.
What is their major function?
Journalists work with general issues or in specific issues. They inform the public about events the public would not know about.
That means they are source of the news we listen to 
Correct. A journalist's work is usually called journalism. It can be written or spoken form.
What more do you know about a journalist?
Most journalists specialize in certain areas that span many topics. For example there are sports journalists.
And? 
A reporter is a kind of journalist that researches, writes, and reports on news or other information.