Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column

Question

I'm trying to make this work but looks I'm doing something wrong, I've already looked around and can't find or figure out a solution! Sorry I'm just new on programing; Got 4 tables and I need to pull some information out :

From table 1 (worksheetsDetails): I need the product_id product_designation and SUM(product_quantity) ordered by product_designation.

From Table 2 (worksheets): I need to get the worksheet_id from where the table 1 are related.

From table 3 (products): I need to get the product_price from products who are in the first table and pull a sum of all the products together where the table 4 (work_sites) worksite_id is related.

worksite_id from worksites is related to worksheets table.

I came this far:

SELECT 
    product_id, 
    product_description, 
    SUM(product_quantity) AS quantity 
FROM 
    app_com_worksheetDetails 
LEFT JOIN 
    app_com_worksheet
ON 
    app_com_worksheet.worksheet_id = pp_com_worksheetDetails.worksheet_id
WHERE 
    app_com_worksheet.worksite_id = '$wsi_id'       
GROUP BY 
    product_description"

And I'm getting that error!

Please someone can hepl?