Catalog Suggestions are a way for you to fix bad or invalid part numbers. A Catalog Suggestions tag with a gray bullet will appear below the part number in the Quoted cell if there are any suggested part numbers.
You don't need to use Catalog Suggestions if the part number has already been recognized (has a Manufacturer listed).
Clicking into the part number section will open up the Suggestions module:
Clicking the graph icon will link you to the Parts Intelligence page for the part. Clicking the two arrow icon will navigate you to the comparison page where you can compare the suggested part with the original part.
CPQ will sort your Catalog Suggestions and External Suggestions by previous usages from most to least used.