You don't need to raise the beds, you can just remove the grass and dig over the soil, but that is really hard work and you will have to dig it every year.
You start planting in March/April.
Basically plants fall into 4/5 groups and you have to rotate these groups so that you don't grow the same group in the same spot each year because the soil won't be good.
Potatoes are by far the best thing to grow first. They will grow in pretty much anything and will break up the soil and make it easy to grow other stuff afterwards.
So this year you need to do the preparation for next years growing, you can either prepare the whole plot and plant all 4 groups first year. Or prepare a quarter and just plant spuds and then add another group each year (as with the raised beds post).
If you want to plant straight into the ground:
1. Work out where your patch is going to be. 2. Remove any turf. 3. Work you way across the patch turning over about 8 inches deep of soil. Keep going till you have done it all. Frost over winter will break it up further and make it easier in spring. 4. Add lots and lots of manure/compost to the section where you intend to grow things from the potato family and add lime (chalk) to the area where you intend to grow things from the bean family. 5. Decide what you're going to grow next spring.
The 4/5 groups and the order you should plant them in:
1. Potato family - includes tomatoes and aubergines 2. Bean family - peas, broad bean, runner beans etc 3. Brassicas - includes turnips, broccoli, cauliflower, cabbage, radish 4. Roots - carrots, parsnips, celery (5. Other stuff which can be planted anywhere to fill in gaps - onions, leeks, sweetcorn, courgettes, lettuce, beetroot)
It's up to you whether you grow one or two things to get you started the first year, or whether you want to grow lots of different stuff. I was chicken so started with just spuds and then gradually added one from each group. Will be venturing out with 2 from each group next year.