Acoplador óptico

Good morning!
I am a student, and I have some doubts arduino!
I have a project in which use an optocoupler, and have to find a function to do some sort of a coalition with the arduino to know if acolplador is HIGH or LOW.
Only I can not find the most appropriate function for this situation!
If anyone can help me ....
THANK YOU FOR UNDERSTANDING

digitalRead?

but the goal was proposed:

  • The arduino detect if the coupler is active!

there is some function "status"?

You connect a pin to a digital pin of Arduino and use digitalRead() to read the status.

How you connect hw to Arduino ?

I guess I'm not to express the problem well! sory