"Full sun" gets thrown around a lot on seed packets and plant labels, but it has a fairly specific practical meaning: six or more hours of direct, unobstructed sunlight a day. It doesn't need to be one unbroken block; four hours in the morning and two more in the afternoon still counts. Partial sun generally means somewhere in the four-to-six-hour range, and shade means under about two to three hours of direct sun, even though a shaded spot might still get plenty of bright, indirect light through the day.
The only reliable way to know what your own garden actually gets is to watch it, properly, through a full day, ideally more than once across the season. Stand in the spot you're considering at a few points from early morning to evening and note when direct sun actually reaches ground level versus when it's blocked by a fence, building or tree. New Zealand's sun angle changes a lot between summer and winter, more so the further south you are, so a bed that gets six hours of sun in December might get half that in June, as the sun sits lower and shadows from fences and buildings stretch further. If you're planning a bed for spring and summer crops, check its sun in spring and summer specifically, not in the depths of winter when the picture is worst-case.
so a bed that gets six hours of sun in December might get half that in June
Fruiting vegetables generally need the most sun of anything in a home garden. Tomatoes and capsicums are both classified as needing full sun, and it shows in how they perform: skimp on sun and you get a leafy plant with little to no fruit, since flowering and fruit set both depend on the plant banking enough energy through photosynthesis. Most of the classic full-sun crops, carrots, beetroot, broccoli, cauliflower, cabbage, kale and peas among them, fall into the same bracket and are worth reserving your sunniest ground for.
Leafy greens are more forgiving, and this is where people often over-estimate how much sun they need. Lettuce grows well in partial sun rather than needing a full-sun spot, and both spinach and silverbeet are shade-tolerant, genuinely capable of cropping in a spot too shady for most other vegetables. Parsley is the same: it's shade-tolerant and one of the better choices for a garden's shadier corners. None of these need the sun to be blazing all day to produce a usable crop.
If your only available space is shadier than you'd like, the practical move is to match your planting to the light you've actually got rather than fighting it. A spot getting three or four hours of morning sun is a poor home for tomatoes but a genuinely good one for lettuce, spinach, silverbeet or parsley. Reserve any full-sun ground you do have, even a small patch, for the crops that need it most, and use the shadier remainder for leafy greens and herbs that will actually crop there.