Learn German: Die Leute sind heute glücklich.

sind is the "they" form of the verb sein (to be). We use it here because the subject, Die Leute (the people), is plural and acts as a "they".

Is Leute always a plural word?

Yes! Leute (people) is always plural in German, which is why it takes the plural verb sind. If you want to talk about just one person, you have to use a completely different word, like die Person.

Why is heute in the middle of the sentence instead of at the end?

German likes to put time words like heute (today) early in the sentence, usually right after the verb. While in English you usually say "The people are happy today," German naturally structures it as "The people are today happy."

Why doesn't glücklich get a plural ending to match Die Leute?

In German, adjectives only get special endings when they sit directly in front of a noun (like "the happy people"). Because glücklich comes after the verb sind, it does not change and stays exactly as it is in the dictionary.