I have two forms. How can I access a textbox on one form from the other form
One way to do this is to make the TextBox either a public property or a public field. Then you will be able to access it through the instance of its parent form. So, if TextBox1 is a public member of FormA and myFormA is an instance of FormA, then you can use code such as
anywhere myFormA is known. Here is a VB project
illustrating this technique.