Building on what you learned in Ser vs. Estar – How to Use Estar, “Ser” is also used for…
Time of Day
Determining Something’s Purpose
Physical and Psychological Traits
If you need to talk about a group or entity you belong to, you’ll use “Ser”. Examples:
Vocês são escuteiros. You are scouts.
Tu és budista. You are a Buddhist.
And there we go! There are a few other ways of using “Ser”, of course, but these should help get you started. The rule to remember is: “Ser” is usually used for permanent conditions, traits, or things.