Planting different types of plants together can indeed help the plants! Some plants will help ward off pests - marigold flowers, onions, and garlic are a few I know of - and some plants are "nitrogen fixers" meaning they get nitrogen into the soil and so planting them next to a vegetable that needs a lot of nitrogen is useful, things like that. Plus, if you DO lose some plants due to pests, if you have them scattered in different areas maybe you don't lose your whole crop of that plant, but just one section.
Good luck with your garden progress! :)