There are so many options of ways for your child to be officially educated. For us, in the preschool years, we have decided to homeschool. Whether you choose to send your child to a traditional, Montessori, Waldorf, or any other school or to homeschool, the very first (and very best) teacher your child has is YOU! There are two very simple things you can do with your child every day that help him learn about the world.
Talk to him. From the day he was born, you have been talking to him. Tell him about the world using lots of descriptive words (colors, sizes, etc). Sing songs to him. Give him an opportunity to 'respond' (even if he isn't talking yet). This helps him learn about conversations.
Play with him. The items you play with can be as simple as a bowl, scarf, or cardboard tube. You can even simple clap his hands together or do finger plays with him (like the itsy bitsy spider).