So you might have heard things like "don't plant two kinds of tomatoes near each other" or "my hot peppers made my sweet peppers taste funny." And you've probably heard that it was because of cross-pollination. Which may have made you think - what is cross-pollination?
Cross-pollination is when pollen from one variety of plant pollinates a different variety. So a roma tomato might have pollinated a beefsteak tomato. Or maybe a green zucchini pollinated a yellow zucchini. Does this mean you're going to get frankenfruit? The answer is no. Your fruit will be fine.
A lot of folks seem to misunderstand what the child of a plant is, and they think it is the fruit. The fruit it just the holder for the fertilized seeds. In people, an egg is fertilized and then starts growing into a child. But that isn't how it works with plants. Their fertilized seeds are inside the fruit. The fruit is still part of the plant it is attached to - it is not a child. The child is what you get when you plant those fertilized seeds.
So what does this mean for my plants? Nothing at all for the parent plant - the fruit it bears will have been in no way affected by the pollination it received. But to the child plant? Lots. If your flowers were cross-pollinated, those seeds are now made up of two different plants. So you may get something odd or even inedible. Squash from cross-pollinated seeds, for instance, may make you quite ill if you eat them. But cross-pollination is also how over the centuries farmers and seed companies have developed new varieties of plants. So it's not always a bad thing. Some folks will purposefully cross-pollinate two plants trying to come up with a plant that has the best characteristics of both.
Now there are some exceptions to this, of course. Some plants, like fruit trees and strawberries, can be quite affected by cross-pollination and it may be preferred for this to happen. But the veggies you're growing in your garden? Unless you are saving the seeds to use next year, you'll be fine. If you do plan to save seeds, then you may need to take measures to limit cross-pollination.