How do you house train a puppy?

My puppy is a shih-tzu/mini american eskimo and she's 4 months old and still not house-trained. It's super cold outside so i don't know if that's why she doesn't want to go out..but we're getting tired of stepping in pee. How can we train her to go outside without having to keep her locked in a crate all the time. We got her for the kids and they really enjoy playing with her.