Your question is slightly confusing but I'll try to answer your question.
As far as I can tell McCoin brand is bags of frozen vegetables (correct me if I am wrong).
If it says do not thaw and to cook from frozen, it just means you do not need to thaw it before you cook it.
Thawing is the act of unfreezing something. This can be accomplished by leaving something out at room temperature to naturally thaw.
So if you have frozen corn and want to put it in chili or soup, just throw the frozen corn directly in without thawing it.
Two Reasons:
1.) The faster the food drops below the 'Danger Zone' the less spoilage it will have
If it takes that freshly-cut steak 2 hours to cool down from cow-body-temperature to a safe 40F, that's more spoilage and less shelf-life for the product. A rapid chill-down means a more valuable product.
2.) Ice-crystals damage food, and the faster water freezes, the smaller the ice-crystals
If the temperature of the water drops slowly, the water-molecules will have time to organize themselves into nice, neat rows (imagine a big snowflake). At a microscopic level, these ice-crystals will puncture cell-membranes and cell-walls, damaging the food and affecting texture.
If, on the other hand, the temperature drops rapidly, the ice-crystals will form more haphazardly, with less well-organized crystals. This means fewer ice-javelins stabbing into your food.
Try an experiment sometime: take a serving of ice-cream out of your freezer, let it melt completely, put it in an airtight container, then toss it back in the freezer. Let it freeze completely and taste it. The flavor will be roughly the same, but the texture will be much worse. There will be big, crunchy ice-crystals throughout.
The big-time ice-cream makers invest in heavy-duty freezing tech that allows them to freeze the ice-cream faster, and with smaller crystals, the less-granular, and more creamy this tastes.
Best Answer
If this is just raw seafood, and not already prepared, heat and serve meals, keep frozen until use. Thaw (ideally in the refrigerator), then cook. If they are meals already prepared (with other ingredients), simply follow the package directions. Many of these items are cooked from frozen.