I'm trying to grasp the concept of how IPFS works. Say if I upload 1GB of data to IPFS. How long does it stay there? Or do I have to leave my computer on at all times for the file to be live on the IPFS system? If thats the case, why don't I just host it myself. What about SWARM? I'm trying to find a decentralized file storage system where I can upload once and it stays there forever.
IPFS doesn't solve the persistence problem for you, the only way currently to ensure that your files will exist is to
pin them on an IPFS node, which means you need pin rights on that node. Run your own node, there are a few services out there that you can pay to pin content, find a node that will volunteer to pin your content, or wait for Filecoin which solves the problem by allowing you to pay Filecoin for persistence.