That a baby is crying is only natural, but also heartbreaking for the parent. There are many, completely different reasons for why babies cry. Some of them might feel very random; others indicate that the baby might be sick. Always try to comfort your baby as soon as you notice that something is wrong. If there are no other symptoms, your baby will be just fine.
There are three main causes why a baby is crying: it is hungry, sleepy or needs a change. These are simple things to check for and there are also simple cures for them. The most important thing, while you change your baby or feed it, is to remain calm and talk soothingly to your baby.
Other reasons for why a baby might cry include a lack of closeness and comfort, that it misses its parents or that something is wrong. When comforting you baby when it is crying, you will soon notice that the crying will stop by itself after a while. Whatever it is that is wrong (and whatever it was, there might only be baby logic for the crying), is now good again. Lack of attention is a very good reason for babies to cry.
You will soon learn to understand why your baby is crying and what you can do against it. That is why you need to be extra alert when the baby is crying for a reason you do not understand. Then it might be telling you that something hurts or that it is in pain. Reasons for this might be an illness, such a fever or colic. It can also have stomach pain or it might just have fallen down after have been trying to stand up.
Attention is very important when soothing you baby. This is how you will notice what is wrong and also teach your baby not to cry for reasons such a being alone and needing comfort. When you show your baby that you are there, it will automatically put more trust in you and cry less.
If your baby cries and cries and never stops, be sure to seek medical advice. Your baby might then be acutely ill and need medications.