Such a trouble-maker. I’m not exaggerating when I say that this one causes more head scratches than all the other punctuation marks put together.
Understanding that the apostrophe has two very different uses in English – possession and contractions – could save you, and your readers, a lot of grief.
It’s nice to see you. (contraction)
The carpet is dirty. Its softness is gone. (possession)
You’re smart. (contraction)
Your house is beautiful. Its features are exquisite. (possession)