How to get the session_id from the vault for payment

[sehajdeepsingh]

In the image above, it says we need to set payment.session_id, however, I am unable to find a way to get the session_id? 

basically upon a click of a button:

1. I want to create an order,

2. then create a checkout,

3. collect a payment***, and

4. then complete the checkout.

*** This step requires to populate the session_id, how to get the session_id from the vault?