Using arguments from different tables in one formula

Please help me to understand how to do thing that can be easy done in Excel. I have 3 tables:
1st is the list of customers and their orders. For example с1 ordered 1 pc. of g1 and 2 pc. of g1:

2nd is the list of gs (g1-g3). For example g1consists of 0.5 pc. of part1, 1,7 part2, 23.4 part3…

In the 3rd table i want to have list of clients and sum of parts that they ordered:

Airtable isn’t really designed for the standard “spreadsheet” data structure you’ve shown. To do this you’ll want to adopt a more database friendly approach by linking records together. Essentially, you’ll want one table for each “thing” (one for Customers, one for Orders, one for Products, and one for Parts), and one table for select relationships between things (one for Product Assembly noting how many of each part are in each product, one for Line Items noting how many of each product have been ordered for each order).

Here is a suggested database structure:

Depending on how many Parts you will ever have, it may make sense to keep the portion of your current strategy where in your Products table the quantity of each part per product is recorded using Number-type fields as opposed to using an Assembly table as in my example. If you only need a total of how many of each product has been ordered by each customer, you can get away with deleting the Orders table and instead link Line Items to Customer directly.