How to use Summation User-Defined Attributes

Summary: How to add the amounts of the lines of a purchase agreement to send an approval flow

Content (required):Our client requires that approval flows for purchase agreements be generated according to ranges of dollar amounts and category names.

For example, it presents the following approval ranges

from 0 to 10,000 dollars with same category name 
from 10001 to 100001 dollars with same category name
From 100001 to 500000 dollars with same category name
Greater than 500,001 dollars with same category name

The problem is that the system only approves the amounts per line and does not add up the categories.

In the system there is the option to create sum attributes generated by the user. The question is how to configure this attribute?

For