A quick search on the internet for 3 tier architecture will give you a lot of information on the best practices for developing applications for multiple users. The following image should give you an idea of the 3 tier architecture . If you have a very basic application then you could get away with a 2 tier application with the application on the desktops connecting directly to a single database server. But using the 3 tier model is the recommended and correct way to do this.
A starting point would be an article like the one found here. http://www.codeproject.com/Tips/662107/Understand-3-Tier-Architecture-in-Csharp