How to find variance between columns from separate tables

Here is my data: https://ibb.co/1bH6QSF

I am trying to find the variance (difference) between the first and middle table in terms of expected sales and sale total (these are the actual sales), at the product category level (Table 3), for each year, quarter, and month.

How would I go about doing this? I suppose there are two preliminary steps:

1) Create a date-variable that links to the 3 tables.

2) Create a model that links the three tables together

The given date variables are weird, however, e.g. in table 1, I have "Year" and "month" in two separate columns. How do I consolidate this?

Ultimately, I want to create something similar to this: https://ibb.co/r4rgDfS

That can show me the "actual sales"  (total sale in my data) vs "target sales" (forecasted sales in my data), at a Year, quarter, or month level.

Any help is appreciated, thank you!