A feeling is a human state. We often experience feelings as something bad or something good. We know feelings like fear, joy, sadness or love. Sometimes the feeling comes from within ourselves, sometimes it is a reaction to a stimulus from outside.
Sometimes a feeling comes from something being wrong with the body. For example, if the brain is not functioning properly, someone is always very sad. If the feeling lasts longer, it is called depression. In certain cases, the doctor can prescribe medication to help.
You can often tell how a person is feeling from the outside. For example, you can see it in their face or hear it in the sound of their voice. If someone is sad, they may be crying. If someone is happy, they may have a smile on their lips.
One speaks of gut feeling when one reacts immediately to something without thinking. This comes, for example, from feeling uneasy. It can also mean that you think something is quite normal and right.