SharePoint Add-in Crude Operation

I am completely new to the SharePoint Add-in Development.

For Add-in Development I am using VS 2015, basically want to create a web site in Share Point to Add, Modify and delete operation from the Share point list. I want to create a web page where I should get an option to add, delete and modify the data in the Share Point list.

Till now I have created the Apps using Visual Studio

New Project >> Visual C# >> Office/SharePoint>>Web Add-ins>> SharePoint Add-in

in Next Window using SharePoint-Hosted then SharePoint online

then In Default.aspx added label and Text box

<asp:Label ID="Label1" runat="server" Text="Enter User Name"></asp:Label>
&nbsp<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><br/><br/>
<asp:Label ID="Label2" runat="server" Text="Enter Password"></asp:Label>
&nbsp<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>

Not able to get how the take the textbox value to the SharePoint list.

Thanks in advance for any help.