If it seems strange to talk about ideas or ideals as somehow more real than the world of our experiences, consider science. Ideas are available to us through thought, while phenomena are available to us through our senses. So, naturally, thought is a vastly superior means to get to the truth. This is what makes Plato a rationalist, as opposed to an empiricist in epistemology. Senses can only give you information about the ever-changing and imperfect world of phenomena, and so can only provide you with implications about ultimate reality, not reality itself.
Reason goes straight to the idea.
You remember, or intuitively recognize the truth, as Socrates suggested in the dialog Meno . According to Plato, the phenomenal world strives to become ideal, perfect, complete. Ideals are, in that sense, a motivating force. In fact, he identifies the ideal with God and perfect goodness. If the world is not perfect, it is not because of God or the ideals, but because the raw materials were not perfect.