You can simply drag and drop Tab Control from tool box of VisualStudio.

Coding of controls present in tabPage1.

  private void rdoRed_Click(object sender, EventArgs e)
        {
            this.BackColor = Color.Red;
            gbColor.ForeColor = Color.Red;
            btnDefault.ForeColor = Color.Black;
        }
        
        private void rdoBlue_Click(object sender, EventArgs e)
        {            
            this.BackColor = Color.Blue;
            gbColor.ForeColor = Color.Blue;
            btnDefault.ForeColor = Color.Black;
        }
 
        private void btnDefault_Click(object sender, EventArgs e)
        {
            this.BackColor = DefaultBackColor;
            gbColor.ForeColor = DefaultForeColor;
            rdoRed.Checked = false;
            rdoBlue.Checked = false;
            rdoGreen.Checked = false;
        }
 
        private void rdoGreen_Click(object sender, EventArgs e)
        {
            this.BackColor = Color.Green;
            gbColor.ForeColor = Color.Green;
            btnDefault.ForeColor = Color.Black;
        }

Coding of controls on tabPage2.

        private void treeView1_NodeMouseClick(object sender, TreeNodeMouseClickEventArgs e)
        {
            TreeNode nName = e.Node;
            string webPage = "";
            webPage = (string)nName.Tag;
            if (webPage != "")
            {
                webBrowser1.Navigate(webPage);
            }
        }