How much SS benefit is taxable when collecting SS at Full retirement age but also Working & receiving an income

I understand there is no limit on how much you can earn and still receive full benefits after full retirement age.

 

I don't understand how much of my SS benefit I am receiving will be taxable - all of it or a percentage?

 

Also, if I am earning an income from an employer and SS tax is being taken out of my pay, does the SS benefit  I am already receiving get increased at some point by what is being held out of my pay?

 

Thank you.