Retirement tax questions

BUT if it is taxable because I have some extra income that I report? What is taxable?

That is my question.

Let's assume my earned income + SS benefits is well over 25K.

Do I pay any tax at all on that first 25K or just the amount that goes over 25K.

If it's like the IRS tax tables for income tax returns, I guess you are paying taxes on the entire amount? 

 

Oh ... and add in the personal deduction and I have no idea what I need to pay.

 

I really don't want a surprise at tax time, or a penalty for not withholding.