I have no knowledge of modding. What does this mean?
The Creation Kit is the set of modding tools that has made Skyrim modding so prevalent compared to most moddable games. You can technically mod the game without it, but it opens up modding to basically anyone willing to put a little time into learning even just basic level design and/or scripting, as opposed to being mostly the realm of actual programmers.
The CK also standardizes the storage, installation, merging, etc. of mods to a huge degree (mostly through intermediaries like mod managers, admittedly), which allows the nice, insane situations where people have 255 plugins running (and probably a few hundred more mods merged into those) and the game still mostly runs without imploding.
Edit: The 32 vs. 64 bit thing is mostly going to be a pain to the middleware modders (Nexus Mod Manager, SKSE, etc.) I imagine, and probably won't have huge impacts on the end-user modders (people making weapon models and the like) aside from them having to wait for the tools to be updated, which will probably be waiting on the Creation Kit to be updated.