The Catechism goes into some detail on those issues:
Grave matter is essentially something that in itself is very evil like murder, rape, adultery, etc.
Full knowledge means you either know it is grave matter, or should know (eg you should know drunk driving is gravely irresponsible).
Full Consent of the Will is misleading considering the fact we live in a fallen world there is rarely such thing as “100% full” consent, a better term is “sufficient” consent meaning you know you could have chosen not to sin on something that was grave matter but you did sin anyway. Also this teaches that you cant be forced by another person to commit grave sin.
Those are the general guidelines.