Peas and beans are the seed pods and seeds so they need to be pollenated by insects; the same with courgettes, marrows, squashes. Because you want them to flower then produce seeds if you need to use fertilser you should use one which encourages flowering, eg one with potash in it. That was what I meant when I said that growing veg isn't that different from growing other plants, just work out whether you're growing flowers or foliage.
Cabbages, sprouts, lettuces, leeks, broccoli, onions, etc you eat the leaves - you don't want them to flower at all - you want to encourage plenty of leaf growth so they don't need the potash, they need nitrogen - eg chicken manure pellets. If this sort of veg is checked while growing, by a dry spell for instance, the plants might 'bolt' that is send up a flowering stem and 'run to seed' which you don't want to happen, so try to avoid letting the soil dry out completely.
Root veg don't like freshly manured soil - it makes the roots fork and become deformed, so grow them in soil that was manured the previous year.
Also, I don't want to give the impression that you need to be giving veg loads of fertiliser all the time - a good manure/compost dug in iduring the autumn or early spring is usually all that is needed
