When do IRS liens have to be paid?

[Account Closed]

Hello, and thank you for taking the time to read this!

I am new to real estate and am having a blast learning. Hoping to make my first deal soon and stumbled across a local auction that might help me. I am looking at some properties at the county tax auction, one of which has a substantial amount of IRS tax liens attached to it. My understanding is that the IRS tax liens will have to be paid, but when? 

Will they need to be paid at the auction along with whatever the house sells for, before the deed can be transferred into my name? Or will I have to pay the liens off later, before I sell the property?

Thank you for your time!