The most important thing is to check the food label on the back of the packet. Check out this article on food labels.
In general, it is important to choose foods with less than 10g of total fat per 100g. For milk, yogurt and ice-cream, choose less than 2g per 100g. For cheese, choose less than 15g per 100g. Finally for the unhealthy saturated fat, aim for the lowest, per 100g. Less than 3g per 100g is best.
For more info on this check this out: https://theconversation.com/mondays-medical-myth-low-fat-diets-are-better-for-weight-loss-11586.