Q.what plant food or fertilizer to use for caster bean plants?
I’m new to gardening and want to know what to feed my plant. I’m starting out from seed.
Castor beans are easy and vigorous; here's more about them: https://www.gardeningknowhow.com/ornamental/foliage/castor-bean/castor-bean-information.htm
If the soil is even marginally fertile, you probably won't need to worry about fertilizer. If you really want to use some, an all purpose 3-1-2 formulation, or balanced 1-1-1, would be fine. Learn more about fertilizer here: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-npk.htm
One thing you will find helpful as you begin to learn about gardening is to understand that plants make their own food by using the energy in light to combine elements from air, water, and the nutrient minerals in the soil. Fertilizer just helps along what's already there. So the starting points are always correct light for the type of plant, correct water, and good soil. You might want to start by learning about soil, and how to nurture it. https://www.gardeningknowhow.com/composting/basics/ultimate-beginners-guide-composting.htm