When is criminal conspiracy said to be done by a person?

As per IPC Two or more persons agree to do, or cause to be done, an illegal act, or an act which is not illegal by illegal means, S. 120A. Definition of criminal conspiracy: When two or more persons agree to do, or cause to be done, (1) an illegal act, or (2) an act which is not illegal by illegal means, such an agreement is designated a criminal conspiracy: Provided that no agreement except an agreement to commit an offence shall amount to a criminal conspiracy unless some act besides the agreement is done by one or more parties to such agreement in pursuance thereof.