Do you have to be invited to write a review? I am interested in writing a review on a topic that I am very interested in and am very well informed about. I would like to ask how does one go about doing this? 

I was told that you have to be invited by a journal to write a review or else you give a talk at a conference and they ask you to write a review. You can't just decide to write one and submit to a journal. If this is true, I am confused as to how one would do that, as at all of the conferences I have attended, presenters usually give an entire story with results and not just update the audience on the literature.

Any ideas or suggestion on this would be greatly appreciated.
As with any submission it depends.  Your advisor should be able to answer this question for you field.

I would highly recommend NOT writing it unless you have either been invited to write one by a conference editor, or your advisor says its common in your field.  Many journals/publications are very hesitant to accept these kinds of papers as any number of experts could write them fairly quickly, and your field likely doesn't need several "survey" papers.

Whats more, any sub-field really only needs one good survey paper published every few years to make sure all its readers know the state of the research.  You're also not the only researcher who has knowledge and interest in writing this paper, so the market is likely pretty crowded.