get a value from another form in the C#

Forms are basically classes where you can put variables to. So you can do something like the one below on your destination form

Suppose you have this class that you want to pass from your source to destination

public class Product
    {
        public Product() { }
        public int ProductID { get; set; }
        public string ProductName { get; set; }
        public double Price { get; set; }
    }

On your destination form, declare the class that will contain the passed object

public partial class Form2 : Form
{
    public string val; //added variable
    public Product product; //added Product class
    public Form2()
    {
        InitializeComponent();
    }

    private void Form2_Load(object sender, EventArgs e)
    {
        //Do something on val and product
    }
}

And then on your source form, you put values on the variables and on the object like below.

Form2 frm2 = new Form2();
var product = new Product();
product.ProductID = 12345;
product.ProductName = "";
product.Price = 12.0;
frm2.val = "Test";
frm2.product = product;
frm2.Show();

OP wrote:

how i do define my data type or object ?

Not sure what you mean by that, but if you mean passing your objects from one form to another, yes it is possible and the process is the same with the one above.

Edit: I have added a Product class that will be passed from source to destination. Hope you find it useful.

From1:

Button_click(object sender,Evenargs e)
{
string product="AAAA";
int productID=001;

Form2 obj=new Form2(product,productID);
obj.show();
this.hide();
}

Form2:

public Form2(string product,int productID)//Constructor..
{
txtprod.text=product;
txtprodID.text=productID;
}

Hope it helps....