Well......I know it for 2 reasons. 1. Your shoes are wet. 2. The floor, does not react well with the friction of your shoes. 3. You probably need new pair of shoes.
some are, especially the chucks, but Jack Purcell makes some leather ones as well. but they are uber expensive
Some people like wearing socks with leather shoes, and some do not. It comes down to personal preference.
If they are the shoes of one lady, it's lady's shoes. If the shoes belong to more than lady, it's ladies' shoes.
Try water, and if that doesnt work .. leather cleaner .. if all else fails, try alcohol, but i do now know what that would do to the shoe.