In the unfortunate event of your domain going into the redemption period after it has expired, you will be required to pay a redemption fee in order to make your domain name active again.
The redemption fee for different domains can vary depending on the domain extension, you can find out pricing for each TLD on the Domain Price List page.
The exact redemption process varies depending on the extension, some like .EU or .ES have no renewal grace period and enter redemption immediately.
Most gTLDs will have a renewal grace period of 30-40 days before they enter redemption.
If domains are not renewed/restored before the end of the redemption period they will enter a pending delete period where it is not possible to recover the name before it re-enters the pool of available domains.