I don't know what your seed is, but I'm getting a bean vibe from it. Maybe a fava bean? I would agree with SouthernGardner that it seems unlikely to germinate, but I am all for experimentation.
I would buy or make a seed starting mix. This is a growing medium that lacks soil and has nutrients beneficial to seedling plants. You can buy these at a garden center or make your own. You can read more about seed starting mixes here. Generally, seed starting mixes contain peat moss, perlite, and compost. Planting in a seed starting mix will at least allow you to find out if your seed is viable, after that we can help you figure out how to best care for your seedling/future mystery plant.
You want to avoid using garden soil because pathogens in the soil can harm your seed, you may accidentally grow competing weed seeds, and soil is often too dense for tiny seedling roots to easily establish.
Finally here is some general advice about starting seeds including, water, light, seed starting mixes and so on.
OK...how long have you had this? It's been my experience that if the seed was more than two years old, it's generally a no-go. Less than a year is another story. I have some milkweed blooming in my front yard as we speak (I planted it for the butterflies and hummingbirds). The seeds were about a year and a half old when I planted them. However, we planted some Echinacea in there with it (which I'd had about as long as the milkweed), and it wouldn't grow. If you're unsure, you could just try it and see. I'm sure your friend would understand.