Start by creating a new Google Doc. Share this document so others can also modify or edit the document. Sharing can be done either privately and inviting others, publicly requiring the use of a Google login, or publicly for anyone anywhere.
A nice tip is to create a table inside your Google Doc. A nice table is 2 columns by many rows. Since anyone can write anywhere, ask students to write in a particular row, making it more organized and easier to get started. Table properties allow you to change the color of the table and outline size of cells.
After the initial writing is over, students can quickly comment on other students ideas by adding text into the appropriate box.