How to add multiple values for one attribute?

How to add product attribute in Opencart so that I can get specification of a product as following.

Made of material-------MaterialA,MaterialB,MaterialC
Color---------------------Red,Blue, Green
https://trackeasy.fun/usps/ https://showbox.tools/
Following more I am looking to implement.
1) in search page when user applies RED as filter then the product should come in search result
2)and when user select GREEN then also product should come in search result.
I am using opencart 1.5.6.4

Already checked here on such ?
https://www.opencart.com/index.php?rout ... ute values

To add product attribute in Opencart, please check the below-mentioned extensions:
https://www.opencart.com/index.php?rout ... n_id=32007
https://www.opencart.com/index.php?rout ... Attributes