How can I let multiple users update a single worksheet over a network? e.g. how can I let different users simultaneously (on a network) add new rows to existing rows of data?

I know there's a function called Share Workbook under the Tools menu. What happens if two users attempt to add data to row 10?

How do I deal with a situation where a user has added data to a row e.g. row 10; and another user seeing row 10 as blank and attempts to add data to row 10?

VBA Answers are also welcome