This is the 4622nd most frequent Portuguese word.
decida
"Decida" means "decide" (command form: to make a decision).
Here, 'decida' is used as a formal imperative to ask someone to make a choice.
Por favor, decida qual vestido você prefere.
Please decide which dress you prefer.
'Decida' is used in the subjunctive mood, expressing a wish regarding someone else's decision.
Espero que ele decida logo qual caminho seguir.
I hope he decides soon which path to take.
'Decida-se' is used reflexively to indicate making a decision for oneself.