Yes you can just add ice to your coffee if you want to drink ice in coffee.
However adding ice to coffee doesn't actually make it a real iced coffee but ice in coffee can be good.
Sometimes when I want a cold coffee drink I will add my milk to the coffee and then ice and have a nice icy coffee.
To make an actual iced coffee like you buy you need to add cream, sugar and the ice to make the real iced coffee.
But even just adding some ice to coffee is a good thing.
I also like to sometimes get a glass of milk and add some ice cubes to the milk which makes a nice refreshing milk drink.