A conspiracy requires more than just talking about a crime. It requires an act toward committing the crime. This is known as an overt act.
The overt act itself does not have to be a crime. For example, if two people discuss robbing a bank, they haven’t committed a crime yet. If one of them later goes to rob a bank and the other stays home, only the person who actually robbed the bank gets charged. However, if after they talk, they go to a store and buy ski masks to wear during the robbery, that’s an overt act. Even if the person who paid for the masks stays home while the other robs the bank, both have committed conspiracy to commit bank robbery.