Hi,
Filters are a whole new world.
You might like to start with a tutorial (
http://www.digitalcameraworld.com/20...ced-exposures/) just to get you started.
Then, rather than just amass huge quantities of glass (or resin) 'just in case', think about what you want to do and what filtration you need to do it. There's no getting away from the fact that in time you will end up with a large collection, but at least you'll know exactly what you can do with each and every one.