The words "cũng" and "đều" stand after the subject and before a verb or adjective to express the unity of the action or characteristic.
"Cũng" shows that something has the same quality or performs the same action as another subject, like "also" or "too" in English. For example: "Linh nói tiếng Việt. Tôi cũng nói tiếng Việt." ("Linh speaks Vietnamese. I also speak Vietnamese."
"Đều" is used after a plural subject to show that every member of the subject shares the action or characteristic described by the verb or adjective, like "all" in English. For example: "Bạn cũng nói tiếng Việt à? Thế thì chúng ta đều nói tiếng Việt." (You also speak Vietnamese? Then we all speak Vietnamese."