question about cc, mods, and other stuff

ok so CC is stuff you download from non EA creators right? and mods are game modifiations that change the game play? i have never downloaded any mods, and i have some CC (i think) from the exchange (sims with clothes and body types not provided by EA). but i'm interested in mods. I have seen some homes on the exchange where you can put objects through walls to change the use and look of them eg. a coffee table placed through a wall so it creates a smaller surface in each room, just as an example. I'm assuming that whoever made it used some sort of mod? because i tried it and it won't allow to be done. anyway i found some mod pages and was also wondering how it would change my games that i download from here. i use the fixes from here to update and download store content from the media fire site. also how do you get rid of a mod/CC if you don't want it anymore? can it ruin my game? any information would be helpful considering i don't know much about this thanks for all!