CrosuS has advanced substantially since its first release. Recently we've added a "Submit mod, map or game" tool to the interface that makes it extremely easy to upload files to CrosuS. The simplest method is to upload your files from within CrosuS itself - and there's a full tutorial here that explains how.
However, even if you choose not to download and use CrosuS, you can still ensure your mod reaches as many people as possible by uploading via the web interface here.
CrosuS traffic is set to grow significantly over the next few months, as we've recently been featured in both the UK and USA magazine PC Gamer.
To download CrosuS, please visit the CrosuS website, or get the files from ModDB.