Welcome to gardening! You can filled a raised bed with good compost mixed with your regular garden soil half and half. If you do not have compost you can purchase it in bags from a home center store. You can also look for bags of soil that are marked as made specifically for raised bed planters. This soil mix will drain well but still contain organic matter to hold moisture. Be sure to add a slow release plant food like Osmocote at planting time to ensure that your new plants have all the nutrients they need. Keep growing, Marianne Binetti