Want to disapper input textbox default value

Want to disapper input textbox default value

Please not give a negative vote if I am Wrong to asking the question. I
have a textbox like that
input type="text" value="user name"
<input class="login-inpt" runat="server" name="loginName" type="text"
value="User Name" />
It hold currently default value, I want that when i click on textbox than
the hold value disapper and cursor comes on that place. thanks to all.