TextBox in c#

Set the TabIndex property of the textbox to 0. That way when the form is loaded it will start up with the cursor in that textbox.

I am not sure I understand your question. I am going to guess that you want make sure your TextBox has focus when your form loads. If so, just use the textbox1.Focus() method in your form's Activated event. You also need to put some some code around it to make sure you don't set the focus every time the form gets activated. Very import in MDI apps, and still important in SDI. You basically want to set a global bool to indicate that you have shown the form the first time so you don't do it again.

textBox1.Focus();