Hello Interloper!
Menu
You can find calorie information on food labels, usually broken down per portion, per 100g and per pack. Per-portion information may be more useful than per 100g but remember that the portion size you're having might not be the same as the manufacturer's portion – this can make a big difference to your calorie intake over the day.
To begin with, it may be useful to weigh the portions you have. This should start to give you an idea of how many calories you are having and whether you need to adjust your portion size.