moding

I basically need major help in figuring out how to mod. I've watched videos, read through the forums here and I'm stuck. Maybe a bit afraid to mess up my computer. I have downloaded SMAPI. I tried downloading via nexus mods and nothing worked for me. The mod folder will not show up for me...

The Day (in game) after fully completing all the Bundles in the community center. When I exit the center it changes from looking normal to looking like Pam's house. I have a lot of mods and have tried removing all the mods that I could think of that would change the building. But none of them...