The precepts of the Church are the requirements of the church that are deemed necessary for you to fulfill upon pain of mortal sin. Mass is one of those requirements, but there are a few situations where you may be excused from Mass.
If you have a debilitating illness, you may be excused from Mass, or if there is extremely bad weather that would make your attempt to getting to Church unsafe, you are excused from attending. The bishop from some dioceses will announce a dispensation from attending on Sunday if travel conditions are unsafe. In some cases, priests may cancel Mass in order to preemptively protect parishioners from harm.
If you are traveling and you cannot find a Catholic Church nearby or cannot make it for a good reason, then you may be excused from attending Mass. You should check with your priest to make sure that your reason was valid and that you did not commit a mortal sin. You are required to be in a state of grace when you attend your next Mass and to participate in Holy Communion.
If your reason was not acceptable by the Church, you will require absolution by your priest.