What's a reliable way to count calories?

I’m trying to minimise my caloric intake, and I’m looking for a way to ascertain how many calories are in what kinds of food.

I know there are websites, phone apps and so on, but they all seem to give me different answers. And how do I know whether the pancake I ate is the same size as the pancake listed on the calorie counting website? In other words, how do I standardise?

How many calories should I be getting in a day? (I’m female, 5’1”, 21 years old.)

For example, today I had two banana pancakes for brunch and a plate of pasta with tofu, vegetables and pesto for dinner. Is that good/bad? Too many calories?

Sorry for all the questions… any help would be greatly appreciated!