Adding a custom control in visual web part

Anand,

Register the control at the top your Visual Web Part ascx file with Register tag:

<%@ Register 
TagPrefix="demo" 
Namespace="ControlsDemo" 
Assembly="ControlsDemo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=01374ea14aa626aa" %>

where Namespace should be namespace of the control's class file.. You can get the PublicKeyToken by using Visual Studio Command Prompt and writing following command:

sn –T "Complete dll path"

Once you registered the control, you can use in your Visual Web Part as follows:

<demo:ServerNameControl runat="server" id="serverNameControl"/>

PS: Please follow Kirk Evan's following post
User Controls and Server Controls in SharePoint