There's so many various ways to enlighten your mood and express your sadness, meaning it's too vague to put one statement and claim it as the exact thing you should do when feeling sorrowful.
However, I'll list a couple common things to do when you're sad:
spend time with people you love to make yourself happy
do hobbies to distract yourself from sadness
let all your negative emotions out by crying or some other method, so you don't have to feel it later
listen to your favorite songs~ it's said that music can lower your cortisol levels, ease pain, and inspirit your mood
Putting this aside, I hope you're doing alright! I'm a bit confused if you're asking this on your behalf because you're a bit down, or it's for some homework question, but I'll give you some gentle reminders:
Make sure to give yourself some me-time
You, your opinions, your feelings matter and are valid
You’re important
You’re loved by at least one person in this world. If you can't seem to find that person, I'll be one of them!
