how to create dll file

create a class library project choose the languag whatever you want (C#,vb...)write whatever logic you want then build that library by right clicking the solution you can get the dlls of that project in bin folder of your project.

their are two option to build the project in release mode/ debug mode. it will always better to chose release mode when you are going to deploy

or

see these links
http://www.c-sharpcorner.com/uploadfile/mahesh/dll12222005064058am/dll.aspx[^]

DLLs is a great way to reuse code.

Rather than re-implementing these routines in every program you create, you write them once and reference them from applications that need the functionality:
Creating and Using a Dynamic Link Library [^]
How to: Create and Use C# DLLs (C# Programming Guide)[^]

Building DLLs[^]
How to create DLLs[^]

Right click on ur project add new item select class and write the code in that.then build ur project next right click on your project select Add Refference then select Browse Tab go to your project location then select bin folder then select debug folder in that .dll file extension will be there select that one and click on ok 'dll file is added to your project