⇒ The main purpose of this convention is to find a 4-4 fin in ♥ or ♠. 
⇒ The response promises a 4-card Major, but it can have a 5+card Major if it has both Majors.
⇒ The strength is usually at least invitational, which means 7+ HCP or 2+EHT.
⇒ The responses are quite simple. The opener describes the distribution and waits for the partner's reaction.