如何使用太阳黑子设置具有多对多关系的方面搜索？

I haven't implemented a search feature before and feel a bit stuck. I have a Sunspot search feature which finds results based on keywords - this works great - but I now want to implement the multi select facet feature, but I can't even seem to figure out how to set-up a basic facet search.I haven't implemented a search feature before a