Typically a sharing meeting will open with a standard explanation and then The Twelve Steps and The Twelve Traditions (and often The Twelve Concepts of Service) will be read. After that there will be a small amount of administration. Then chair person (who will often change from week to week) will announce the topic and may provide some literature to start to guide the meeting. Then there will be a chance to share (if you wish). After a set period of time the meeting will be closed.
There is a variation from meeting to meeting as each meeting has autonomy.