how to make the first letters in textbox capital

Private Sub TextBox1_LostFocus(ByVal sender As Object, ByVal e As System.EventArgs) Handles TextBox1.LostFocus
        TextBox1.Text = StrConv(TextBox1.Text, vbProperCase)
    End Sub

you can use following javascript function :

function initCap(str) {
    /* First letter as uppercase, rest lower */
    var str = str.substring(0, 1).toUpperCase() + str.substring(1, str.length).toLowerCase();
    document.getElementById('TextBox1').value = str;    
}

and call that function on onblur event of text box as shown below :

<asp:TextBox ID="TextBox1" onblur="return initCap(this.value)" runat="server"></asp:TextBox>

Handle the TextBox.TextChanged event.
1) Save the TextBox.SelectionStart property.
2) Use the TextInfo.ToTitleCase Method[^] on the Text Property, saving the result in a new string variable
3) If the Text property is different from the new string, set the Text to the new string, and restore the SelectionStart property. Otherwise, do nothing.

If you don't do it this way, your cursor will move to the start of the TextBox every time you type a character (SelectionStart fixes this), or the event will enter an infinite loop (The equality test fixes this)

make a button event
now you make not TOLOWER not TOUPPER you make totitlecase

Dim value As String = "du bi du da"
Dim title As String = CultureInfo.CurrentCulture.TextInfo.ToTitleCase(value)
Console.WriteLine(title)

'output:
' Du Bi Du Da