A .NET Snap To Screen Form like areo Snap

Try this code in your Form move event, this is a quick test code, you can change it based on your requirement.

private void frmMain_Move(object sender, EventArgs e)
{
    if (MousePosition.X < 20)
    {
        this.Size = new System.Drawing.Size(Screen.PrimaryScreen.WorkingArea.Width / 2, Screen.PrimaryScreen.WorkingArea.Height);
        this.Location = new Point(0, 0);
    }
    if (MousePosition.X > Screen.PrimaryScreen.WorkingArea.Width - 20)
    {
        this.Size = new System.Drawing.Size(Screen.PrimaryScreen.WorkingArea.Width / 2, Screen.PrimaryScreen.WorkingArea.Height);
        this.Location = new Point((Screen.PrimaryScreen.WorkingArea.Width / 2), 0);
    }
    if (MousePosition.Y < 20)
    {
        this.Size = new System.Drawing.Size(Screen.PrimaryScreen.WorkingArea.Width, Screen.PrimaryScreen.WorkingArea.Height / 2);
        this.Location = new Point(0, 0);
    }
    if (MousePosition.Y > Screen.PrimaryScreen.WorkingArea.Height - 20)
    {
        this.Size = new System.Drawing.Size(Screen.PrimaryScreen.WorkingArea.Width, Screen.PrimaryScreen.WorkingArea.Height / 2);
        this.Location = new Point(0, (Screen.PrimaryScreen.WorkingArea.Height / 2) - 20);
    }
}

also you have to show that at-least you tried something (even it if it's a broken code), otherwise this like we are doing work for you, instead of helping you.