It's typically known as ‘sour cream’ in English-speaking countries, although apparently the specific product can differ.

In Eastern Europe, it can be added to soups, particularly borscht; works well in some burrito-style wraps (shawarma, spring rolls and such) and on sandwiches, instead of mayonnaise, ketchup or whatever. Or better yet, it goes nicely together with tomato sauces, hot sauces or mustard, especially if not mixed but put next to, so both sauces are tasted together.

But especially, you want to get some crepes, wrap marinated mushrooms in them, and dip into sour cream mixed with strawberry jam. It's fantastic.