Folks opt for raised beds for various reasons. Their 'importance' only relates to your soils and growing conditions -- the same plants grown in raised beds can be grown in the ground.

Some of the reasons a choice is made to raised bed gardening is the current soil condition. Soil that is heavy clay, very low fertility, offers poor drainage or is somehow skewed to a pH extreme may be difficult to work in an inground situation so raised beds filled with imported soils can eliminate that. The soil in raised beds also heats up faster in spring than inground soil and can extend the growing season. Because raised beds offer (usually) easy to reach planting situations, there is no need to walk close to the plants so no soil compaction. They are also easier to weed and may offer other advantages, especially to physically challenged gardeners, by virtue of their height.

Ideally, a new inground planting bed should be started the previous fall. And there are various ways one can go about creating it. Layering damp newspaper followed by a thick layer of mulch or compost is often used. The newspaper smothers any undergrowth/weeds, decomposes during the course of the winter and the whole business lightly tilled in before spring planting time.

Alternatively, if starting now, I would recommend removing as many existing weeds as you possibly can, then adding several inches of compost to the area and working it into the existing soil. Once this has settled, you are ready to plant. You will need to be alert for any new weeds that may appear but mulching after planting can keep them to a minimum.