Mutex implementation in ASP.NET

Hello,

I have developed a Online reservation web application, which runs on a local intranet server.

Upon deployment I got that, if 2 or more user try to reserve seats at the same time, the system is allowing.

Then I found about mutex, But I am finding hard to implement it.

1)Where to code the mutex,
2)which class,
3)How to lock,
4)Hot to release.

I am not understanding bec, this has to be locked globally.

I tried "http://stackoverflow.com/questions/15181058/how-to-add-a-global-lock-to-asp-net-web-application".

Note : app is developed using ASP.NET and mysql.

Please help me.

Thank you.