If you can, it would be awesome to post bugs in the GitHub issues instead of here, but if you want to discuss a bug more, then you can post bugs here in this Bugs category. If they are bugs in particular levels, look for threads on those levels already. If you have time, please make your bug report super great!
It helps to include things like your browser/OS, screenshots, steps to reproduce, code you were using, whether you were logged in, and any JavaScript error messages showing in the console.