A calorie is a unit of energy, and food packs a lot of them. Many beginners hear that they must count every one. You don't. There are several ways to keep track of what you eat, and the best one is the one you will actually keep doing, and that feels fine to do.
Answer three quick questions below and see which approach fits you right now. It is a starting point, not a prescription.
1. What do you want to find out?
2. How much effort can you spare?
3. Do you have a history of disordered eating, or does tracking food make you anxious?
Systematic reviews of people trying to manage their weight have found that those who regularly kept a record of what they ate tended to do better than those who didn't. That does not prove the record itself caused the result: people who keep logs may simply be more motivated. The evidence is mixed on how long it is worth doing.
It also helps to know that self-reported food records are rarely exact. Studies that compare diaries with objective measures find that people tend to under-report what they eat, and food labels are estimates as well. So a calorie count is a rough picture, not a measurement.
Calorie counting is not for everyone. Eating disorder charities such as Beat warn that calorie-focused tracking can be harmful for people with an eating disorder or at risk of one. If you are pregnant or breastfeeding, have a medical condition, or take medication, especially for diabetes or blood pressure, talk to a doctor or dietitian before you change how you eat.
Pick the method you can keep up without stress. A rough habit that you keep beats a perfect log you drop after a week.
None of this is medical advice. It is general information for adults who are new to eating well.