In R. v. Foster, 2018 ONCA 53, Justice Watt for the Court of Appeal for Ontario provides a useful basic overview of the essential elements of a criminal offence, which I have reprinted below.
Every Criminal Offence has an Actus Reus and a Mens Rea Requirement
“Expressed in the Latin maxim actus non facit reum nisi mens sit rea, it is a fundamental principle of our criminal law that a person may not be convicted of a crime unless the Crown proves beyond a reasonable doubt that the person:
i. engaged in conduct in circumstances forbidden by the criminal law (the actus reus or external element); and
ii. had a defined state of mind in relation to the prohibited conduct (the mens rea or mental or fault element).
The external element or actus reus includes all the elements of the offence except for the mental or fault element. As a result, the external element or actus reus can include:
i. conduct (act or omission);
ii. circumstances or state(s) of affairs; and
Sometimes, this element requires proof that the conduct, which occurred in required circumstances, yielded or caused a certain result. On other occasions, less frequent in their occurrence, proof of conduct alone is sufficient.”
The Actus Reus and the Mens Rea Must Coincide
“Identifying the starting and ending point of the actus reus of an offence is important for at least two reasons. The first is the substantive requirement that, at some point, the actus reus and mens rea must coincide.
See, for example, R. v. Cooper,  1 S.C.R. 146.
The second has to do with procedural issues, such as the time frame of the charge and territorial jurisdiction over the offence.
Sometimes, the conjunction or concurrence of the actus reus and mens rea, which makes the offence complete, does not terminate the offence. The conjunction of the two elements essential for the commission of the offence continues. As a result, an accused remains in what might be described as a state of criminality so long as the offence continues.
Bell v. The Queen,  2 S.C.R. 471, at p. 488.
We describe these offences, such as possession, as continuing offences.”