"The birds and the bees" is a common phrase to cuteify the act of doing It. But that is literally the case when it comes to your garden. The pollen from the male and female flowers need to mix. In normality most of this is carried out by bees, insects and birds which why there is great concern - and should be your concern - that the global honey bee population is under threat.
When you are growing vegetables indoors and in greenhouses you might need to manually help the process along. With larger flowers on greenhouse plants you simply take the male flower and insert the stamen into the female and allow the pollen to mix. The female flower usually has the beginning of a fruit behind it, but if you are unsure, touch all to all and you've covered the ground. As a general rule when plants first start flowering only male flowers appear, so be patient and don't think something is wrong if you can't instantly find female flowers. Plants most commonly needing this help in your greenhouse include cucumbers, courgettes, squashes, pumpkins etc.
Plants you keep on windowsills indoors will definitely need a hand in this department and often these have smaller flowers. Chilies, peppers and tomatoes all being in this category. For these either take a q-tip and touch the pollen on each flower which will spread it around nicely. Alternatively a common way of doing this with tomatoes is simply give the plant a shake. The pollen puffs off and resettles doing the job just as well.
Even though its against most Icelanders natural instinct, the best thing you can do is encourage bees and other insects to be in your garden and greenhouse. Honestly, I have never seen so many grown (sorry to say it but) women run hysterically screaming around the place as much as when bees are nearby. Fair enough, one is not overly fond of wasps, but the Icelandic population simply isn't used to the number of insects increasingly appearing these days. Global warming has made it easier to grow things here, but as also enabled bugs to exist where they once couldn't.
Wasps are likely to be more aggressive, and can be a garden pest if you are growing fruit, but there are very very few Icelanders currently growing more than redcurrants here. In general its bees which hang around our gardens. In particular bumble bees, and my garden is simply seething with them.
The 'wild' aspect of my garden is rammed with what I assume to be Californian poppies. I let these run wild and they behave like invasive weeds, prolifically self seeding all over the place. They are relatively easy to uproot so they do not bother me if they spread into the veg patch. They have a cottage garden feel about them - a feel I would dearly love to pursue when I own my own property.
During summer nearly every poppy head has a bumble bee in it. It is perfectly normal for me to see over 30 within one glance. I have purposefully spread seeds around my stolen greenhouse to encourage the bees. In addition there is another invasive weed overtaking the area around the greenhouse - Mint. Its about as high as my shoulder, wafts its scent across the garden and its amazing.
Mint is a lethal plant to let lose in your garden if you like it to look well kept. It spreads like wildfire. For my purposes this has been brilliant. The broken lower glass panes of the greenhouse have been covered with the forest of mint growing there, protecting from wind blowing in. In summer whilst it is flowering it's attractive purple blooms they poke through some of the gaps and attract incredible numbers of bees to find their way into the greenhouse and enjoy the rest of the flowering vegetable plants and help them get jiggy at the same time.