What is toki pona?
toki pona is a minimalist, philosophical, artistic conlang (constructed language) with only about 120-130 words and an easy to learn grammar, by linguist and translator Sonja Lang. You can read more about it in the Wikipedia page and the official website.
My favorite source to learn it is jan Lentan's lipu sona pona, because not only it is a complete toki pona course, but it also links to many other courses, tools and content.
toki pona: the baby way
I plan on making a toki pona course that teaches by using only toki pona. Its name is toki pona: nasin pi jan lili ("toki pona: the baby way"), in reference to how babies first acquire a language by examples, illustrations and repetition, without needing to know any other language first.
You can look at what I've completed so far at this page.
mi wile pana e lipu ni: ona li pana sona e toki pona kepeken toki pona taso. jan lili li kama sona e toki pi nanpa wan kepeken sitelen taso, kepeken toki ante ala la, nimi lipu sona li toki pona: nasin pi jan lili.