1. Jump on a site like CodeAcademy and try teaching yourself a new computer programming language.
2. Teach yourself a new language. A language you have always wanted to learn.
3. Teach yourself a hobby, like playing the Guitar or something.

BTW, for most people, unless you have traveled, Quarantine doesn't necessarily mean you HAVE to stay home and not go outside (I know this kind of goes against the definition, but I hope most will know what I mean). You can go outside provided you practice social distancing. I've been tempted to head out north (I'm in Canada) and do some sight-seeing or explore towns I haven't explored before. Must be a ghostly sight with almost everything being absolutely deserted.