How can I make my own App for iPhones and AnDroids?

I want to learn how to make my own app to put on iPhone and Androids, preferably for free. I don't want to buy some ridiculous programs or manuals on how to do something. If anyone can help, I'm looking for a legit explanation on how to do this. I am a complete beginner at this but am I highly interested. Whether there's a good website with an explanation or anybody has any insider feedback or help, anything information will do. Thank You.