The word "enjoy" is a verb that describes the activity of Maria and her friends on the beach.
In the sentence "Maria and her friends enjoy time on the beach every day of their vacation," the word "enjoy" is a verb.
It is the action word in the sentence and describes the activity that Maria and her friends are doing.
Verbs show actions or states of being, and in this case, the verb "enjoy" shows that Maria and her friends are engaging in the activity of enjoying their time on the beach.