How Multi-user is implemented in Excel?

Editing excel sheets become very difficult when it grows enormously and I have encountered a problem similar to that. I have been facing a lot of issues while working and editing excel sheets alone. Is there any way possible by which I can engage more people into the editing and modification procedures of the task. I have tried various ways but not a single works, whenever some other person tries to open a workbook it denies access.

Kindly suggest an efficient way to deal with the issue and explain the functionality of every single attribute associated so as to get a proper understanding of the feature.