Why make a new thread? Anyway, your professor explicitly tells you in the assignment that equals takes another Card as a parameter. Just compare this->rank with the parameters.rank, and this->suit with the parameters.suit. If both match, the cards are equal.
If you were still wondering about your question in the other thread about(c : Card), the "c" is just a suggestion of what you should name the parameter, and "Card" is the type of the parameter, just like with setCard.