The scene takes place in a Catholic church. A woman is confessing to a priest in the confessional (the small enclosed stall in which a priest hears confessions). She tells him, "Father, forgive me — I've put £10 on who'll be the next Pope ..."
The woman has placed a bet on who will be the next Pope. She seems to think that this is a sin which she needs to confess. Note that although the Bible does not specifically condemn gambling, betting, or the lottery, it does warn us to stay away from the love of money.
1. If you forgive someone, you stop being angry with someone and stop blaming them, although they have done something wrong. • He never forgave her for walking out on him.
2. In English, when addressing a Catholic priest, you say "Father".
According to Wikipedia, gambling on papal elections has at least a 500-year history. Betting on 16th-century papal conclaves are among the first documented examples of gambling on election outcomes. See here for the latest betting odds on who will be the next Pope.