How to call a controller in a javascript

Hi,

I 've lot of doubts listing all of them down.

My requirement is

I need to create a master screen for Po and populate some data in dropdownlistbox with database table values and need to validate form and then save in database using MVC.

I was able to create a BSP and populate it using a model and do validations using javascript .

Now i need to save it in the databas.

I will be calling the same controller as i used initially

to call the BSP

1.How do i call a controller from my BSP in a javascript?

I tried by <bsp call url> but it doesnt seem to work.

2.When does the do_handle_event get triggered

Is it when i write some events and submit the form.

3.What is this Model Data Binding concept?