how to link a button with ENTER key.

If you are talking about Windows Forms then there is a property available at form level for default button. You can set the value of this property as ID of the required button. So when user press Enter key the click event of corresponding button gets fired.

If you are talking about Web Forms then you can add all the controls (textbox, buttons, etc.) in Panel control. ASP.NET has provided DefaultButton property (or similar one) for Panel controls. You can set the ID of required button as default button for the panel. So when user press Enter key through any of the controls present under the Panel control the click event of corresponding button gets fired.

In form KeyDown event write following code

if(e.KeyCode==Keys.Enter)

{

button1.PerformClick();

}