In most cases frozen veggies are blanched before freezing. Blanching is nothing more like boiling fresh veggies and rapidly cooling them off. The process makes veggies already per-cooked. Another thing to consider is that freezing veggies will break the cells (the magic of water crystals breaking the veggie cells) which makes the veggies softer.

So, in general you can swap 1:1 frozen vegetables for fresh with no problems at all. Fruit gets a little bit more hinky since a lot of them get packaged with syrup to help prevent crystallization (which completely shreds the fruit.). If you’re using the fruit in something- like a jam, or compote where it’s going to get cooked anyway, just be aware that it might need less sugar. you can use it whole you might notice them being a bit more juicy than normal, and a bit… uh… frozen-strawberry-esque? They’re perfectly fine, but they’re going to be a bit… weird. (waffles come to mind. we do frozen strawberries and blueberries, as well as black and raspberries.)

In fact, frozen stuff usually retains more of the nutrients and has more to start with than fresh produce. The reason for this is that the facility they freeze them at are generally next to or very near the farms they’re grown at. So they’re picked when ripe rather than green, and then freezing actually is the best at preserving nutrients.

Vegetables are generally blanched, to deactivate enzymes, though, so they’re already partially cooked. Generally speaking, frozen vegetables need to be cooked from frozen, or thawed in the fridge. Peas are notorious in my family. (Step-grandma thawed peas in the sink for a thanksgiving dinner to… unpleasant consequences.) (If there’s any special considerations, they’ll be listed on the packaging.)

Some vegetables are in fact “meant” to be frozen. like heirloom-varieties of carrots. carrots do this thing as a last-gasp of trying to survive, where the convert their starches into sugars; which increases their ability to survive freezing. (fun fact, this is why humans are so keyed to sweet things- sweetness means it’s in season.)

Before you get any funny ideas about carrots from the grocery store… modern commercial carrots don’t do this; its been bred out as a consequence of breeding for other things (mass production value.) but even so, winter crops generally tolerate freezing very well because… well… they’re winter crops and that’s what they’re good for.

Broccoli and cauliflower are both traditionally winter crops, by the way. as are garlic, leeks, kale, a few varieties of squash parsnips, turnips and beets (which like carrots become sweeter with the cold.)

You’ve probably already made your soup, and I hope you did add the frozen green beans. You can put them right into the boiling liquid, stirring to break up any clumps, and increasing the heat until the soup comes back to a boil before turning it down to simmer. Anything saucy works well with frozen veggies. If you’re going to make a fruit pie, it’s a good idea to use a recipe with specific directions, by adding “using frozen berries” or whatever to your search. But in general, I mix the sugar and cornstarch or other thickener and any spices in a bowl, and if the frozen fruit isn’t all stuck together I add it all at once and stir, then let it sit a few minutes and give it another stir before putting it in the crust. And I have foil ready for the crust edge in case the fruit is slow to cook through.

If the fruit or vegetables are frozen into a big lump, microwave a minute and break them up, but generally you want to use them a little icy.