This is the 4456th most frequent Spanish word.
activar
To activate or turn on.
Here, 'activar' is used in its general sense meaning 'to turn on or enable a mechanism or a system', in this case, the alarm of a clock.
Es importante activar la alarma del reloj cada mañana.
It is important to activate the alarm of the clock every morning.
In this example, 'activar' means 'to start or initiate a plan or an initiative', which is the recycling project in this sentence.
La clase decidió activar el proyecto de reciclaje en la escuela.
The class decided to activate the recycling project at school.
In this context, 'activar' refers to 'stimulate or induce a biological or natural process', pertaining to endorphin production by the medication.