Free check in....but it's really like that

[dodago]

Dear guys, good morning,
I would like to have some clarifications regarding check-in for a flight that leaves tomorrow morning at 11:00..
Can you explain one thing to me, is there a cost to reserve a seat regardless, or can you avoid paying other expenses with the free formula?
Honestly, I didn't understand this step well and I'm waiting for your kind information..
Thank you from the bottom of my heart
My nickname Dodago but my name is Augusto