I've had this game for quite some time now, and I love it. But I'd like to try out some mods and see what more I can get out of this game. But I can't get any of the mods I've found to work. I've tried following the instructions that came with the mods, but no luck. Can anyone give me a clue as to where I'm supposed to put the mod files to get them to work? Is "The Little Ones" expansion required for me to be able to use mods at all? Any help would be appreciated.

Welcome to the wonderful world of Steam which has destroyed the open free for all mod community. :(
Most games are very open for modding nowadays but are also only available through Steam which means if you don't buy the game there you can't have access to the mods.

I remember modding communities as very open sites that were available for everyone regarding where you bought the game. Steam completely changed this. Another reason to hate Steam.

Steam's Workshop is the worst. Shitty idea executed even more shitty.