When you "are distracted", you aren't concentrating on something that you're supposed to be concentrating on.

To "get distracted" means to start being distracted. "Get" is used in lots of situations to describe when something starts to happen. Some examples include:

get wet (start to be wet)

get tired (start to be tired)

get drunk (start to be drunk)

If someone continues to be distracted, use "is", "are", "am", "was", etc.:

Sorry, I was distracted. What did you say?