fieldvalidator for textbox

Hi, I am beginner in asp.net , please help me to create fieldvalidator just after each textbox in the same line
<div id="signUphead"><img src="../images/signInHere.png"" width="141" height="33" hspace="0" vspace="0" border="0" align="top" /></div> <ul> <li><span>Initials :</span><asp:TextBox ID="txtInitials" runat="server" Width="150"/></li> <li><span>Age :</span><asp:TextBox ID="txtAge" runat="server"/></li> <li><span>Place :</span><asp:TextBox ID="txtPlace" runat="server" Width="250"/></li> <li><span>Postcode :</span><asp:TextBox ID="txtPostc ...