Does Sims 3 have collection files like Sims 2? I was on the Sims Resource and downloaded a couple of collection bedroom files, but they were all single files. I'm guessing Sims 3 doesn't have collections, or am I missing something?

I know there is, I'm just wondering if it's usable for custom sets.

The Collections folder is usable for custom collections. But unless this collection file is still named in the default way (coll_0xxxxxxxxxx.package) the game cannot write any changes you make to a collection into the file and will create a new file in Collections instead.
But just to make this clear, you downloaded collection files or did you download a set of objects?

I downloaded a collection, which turned out to be a set of files (eg bed, dresser etc.) can I make this a collection file in anyway? Or is there a place where I can specifically download collections as one file so I don't have to sort through beds, dressers, lights etc to find every piece of the collection?
Thankyou for the response

If the creator of the set hasn't provided a separate collection file you'd have to make it yourself. I doubt that anyone else bothered to make a specific collection for a specific set of items from TSR or any other site.
Here's a video tutorial on how to use the Collections function in TS3: https://www.youtube.com/watch?v=uIxtvzrhAV4

Collection files for various Store sets and themed sets can be found here: http://www.thesimalogue.com/the-sim...tion-files.html

What the problem is really, is by going here http://www.thesimsresource.com/down...ory/sims3-sets/ and downloading any one of the "sets", I have to search through every category to find each item from the set, as they don't come in a collection file, which is frustrating as I'm really crap at decorating houses and it'd be nice to download say a bedroom set and be able to go to the collections tab, and find that bedroom set, if that makes sense!

You can sort everything by custom content to make it easier to find.

Yes, it does make sense, and some creators there do offer a separate downloadable collection file, usually listing the links under notes, or somesuch category. I know ShinoKCR and JonSims did. But most did not, and the only option then is to create those collection folders yourself, painful as that may be.

I have a separate user folder that is cc and Store free for this purpose. I only install what I want in a collection in that user folder, create the collection file (Buy/BuildMode filtered by either Store or custom content only) and drop that into the Collections folder in my regular user folder.