Okay, you're using a 401k or 403b plan with your current employer.  If you have former 401k plans from old employers...roll those into a "Rollover IRA."  

Now add another IRA into your retirement plan, the Roth IRA. The Roth is after-tax money.  Remember your old 401k or 403b is "pre-tax," and rolls into s separate rollover IRA... your Roth is after-tax and Uncle Sam won't tax this money as you withdraw funds.  Tax free money!  

Your IRA custodian can help you set up the Rollover and Roth accounts.