I have a question, I'm new to this and I want to know how I can get the condom that the mission asks for.

There's a small store to the left of the church. That's where you buy them, however I'm not sure the requirements to do so. 

If you've completed Bernice's route by the time Lucifer declares you the Messiah, Sylos will be fully available to buy items. The other way to get condoms is to break into the school lockers, some of which have a small chance of dropping condoms.