ELI5 ISS - how does it never run out of oxygen?

Since space has no air in it how can astronauts breathe fresh air inside the International Space Station (ISS)? Do we ship oxygen up to the ISS in tanks? Do we presently have the technology to make a self-sustaining biosphere in space?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community, and specifically the following reddit users whose questions and responses formed the basis of this conversation: twentythousandleague, happythoughts413, masu12, santi871, mvilla & tico_de_corazon   If you have suggestions, comments, or would like to be a guest on an upcoming episode of this podcast, please reach out to us at [email protected].