Learn Portuguese (Portugal): A primavera é bonita.

In Portuguese, you generally need to use definite articles (o or a) before the names of seasons. Since primavera is a feminine word, it takes the feminine article a, making the sentence literally "The spring is beautiful".

Why do we use é instead of está?

Both verbs mean "to be", but é (from the verb ser) is used for permanent, defining, or general characteristics. Saying A primavera é bonita means spring is inherently beautiful by nature. If you used está, it would mean this specific spring happens to look beautiful right now.

Why is the word for beautiful written as bonita instead of bonito?

Descriptive words (adjectives) in Portuguese must match the gender of the noun they describe. Because primavera is a feminine noun, the adjective must also take its feminine form, which ends in an "a": bonita.