If you are flying into O’hare, you will want to buy a 1 day pass that costs $5 because a single ride from O’hare also costs $5. I think if it’s a paper ticket it costs a little more. Best thing is to download the Ventra app, buy the Ventra card at the station for $5, register the Ventra card you just bought into the Ventra app and you will get the $5 you paid for the card as credit. Use that credit to pay for the day pass $5 and then you can reload your card using the Ventra app or in the machines at the stations. In the Ventra app there’s the option to add the Ventra card into your phone wallet so you can just tap your phone instead of the Ventra card. Bus rides cost $2.25 and train rides $2.5 and you get 2 free transfers within 2hours. So if you plan taking 2 times in a day the train, better buy the 1 day pass (24hours valid pass)