Observing others to determine how they are feelings is the first step before deciding what to do with this observation (such as showing concerns for others). It teaches how to get information from facial expression, body movement and voice to infer about someone’s emotional state.
Your little sister is rolling around on the floor giggling
To identify feelings and emotions pay attention to the person’s facial expression; look at the person’s eyes, mouth and eyebrows to determine how they are feeling (smiling when happy etc). Body language can also help you determine how someone is feeling (arms crossed when angry etc). Lastly you can listen to the person, their voice tone will also give you clues.