You've got two options, basically, and more likely one because of how vast the world is.
The first is to acquire them from other players - either by trade, charity, or nicking them off unclaimed land.
The second option is to acquire a
Wild Windsown Weed, for which you will need a couple of skills. The first is Foraging (which you'll want/have anyway as that leads to Plant Lore and then Farming), and the second is the incrementable Exploration (under the skill values section of the first page of your character sheet). The wiki link there has some more specific numbers for you. I'll add that in my experience they're slightly rare, and it'll also take real-life days to get an actual crop started. But that's the way it is.
As far as feeding yourself, your best options at the moment are probably rabbits and chickens (unfortunately), or if there's a water source nearby, fishing. You should be able to construct a fishing pole (if you have the Fishing skill), and equip that with a bone hook and a spindly taproot (found via foraging). You'll have to look for jumping fish, which may require a long hike or a boat. Fishing, fortunately, requires no effort and thus won't make you hungry while you're doing it. Downside being that you may not have a nearby water source.
Also, as a matter of forum etiquette, these sorts of questions belong in the 'How Do I?' forum.