1)    Knowingly enters the dwelling of another without authorization
2)    When he or she knows or has reason to know that one or more persons is present, and
3)    Intentionally causes injury or, while armed with a dangerous weapon, uses or threatens force upon any occupant.

The words in italics refer to the mens rea, or level of knowledge that is necessary with reference to the crime.  Let’s take each one step by step.

Knowingly enters the dwelling of another without authorization
Unauthorized entry of the home of another encompasses what the layperson would think of as trespassing.  If one has not received permission to enter another’s dwelling, it is an unauthorized entry.  This would not typically include, for example, an invited guest who otherwise meets steps 2) and 3).

A dwelling is not limited to a person’s house or home.  It can be a structure where people sleep or reside more generally, so in addition to a house, it could include an apartment or even a hotel.

The term knowingly generally means that the defendant is aware that his behavior will cause a certain result.  If X is aware that he is entering a home and that his entry has not been authorized, this would probably meet the criteria.

When he or she knows or has reason to know that one or more persons is present
In order for a trespass to rise to the level of home invasion, a person must be present in the dwelling that the defendant has unlawfully entered.  In addition, the defendant must have either been aware that someone was at home, or, the circumstances were such that a reasonable person would have known that someone was at home.  Thus the c does not actually need to know that the home is occupied at the time he enters.  It is enough if some hints would lead a rational person to infer it.

Intentionally causes injury or, while armed with a dangerous weapon, uses or threatens force upon any occupant
The home invasion laws have been made with the general purpose of protecting the people inside from situations that involve an armed intruder assaulting and traumatizing the occupants.  While the defendant can meet this step by causing injury to the occupant, it is not necessary for an occupant to undergo physical injury.  Mental trauma could in some cases be enough.  Alternatively, using or threatening harm to an occupant while armed with a dangerous weapon, without actually following through on the threat, is sufficient to meet this step.  Furthermore, note that the injury need not have taken place inside the actual boundaries of the home, if the harm is a consequence of a sequence of acts that came from the home invasion.

Intentionally generally means that the defendant must have used or threatened force purposefully and knowingly.

Defenses
In connection with home invasion, occupants should be aware that state laws vary on the extent of self defense that is permissible in the face of home intruders.  Under common law, the Castle Doctrine generally allows a person to stay in his home and defend himself if an intruder has unlawfully or forcibly entered the home, so long as the occupant reasonably believes that the intruder intends to inflict serious bodily harm or death upon an occupant of the home.  Variations of the Castle Doctrine run throughout many states, and some conditions (i.e. the occupant must not have provoked the use of force) may attach.

On the contrary, some states follow the Duty to Retreat doctrine, which requires the occupants to retreat from the dwelling and verbally announce any intent to use deadly force, before they can be legally justified the use of force through self defense.

“Stand-your-ground” laws, which similar to the Castle Doctrine allow an occupant to stay in the home and defend himself without an announcement of the use of force, are being codified in many states.

Please see an attorney if you have questions about what your state expressly allows.