calculate sum of user's orders in drupal commerce
You can use the view Commerce Backoffice: User orders.


Clone the display users orders.
IN advanced settings, set use aggregation : YES
remove All fields from the display except order Total
In order total field aggregation settings, set type = SUM, group a column = Amount


That's it.

Alternatively, if you don't use Commerce Backoffice module, you can create a view from scratch if you have no user's orders view (I don't remember which default views are provided with Commerce) : 


Create a view of orders
Add a contextual filter Commerce Order:UID
Add a field total and repeat steps above


This should be enough. Remain formatting details...