In Christian churches there is a day of worship, usually Sunday. In the Catholic Church we have Mass. Mass is what @Fauken said. In the Catholic Church is offered everyday, sometimes more than once. I live in relatively small parish, big for our diocese but small compared to a lot of the country, and we offer 8 weekday Masses and six weekend Masses.
There are two parts to the Mass, the Liturgy of the Word, where scripture is read and the homily is given. The same scripture is read in all Catholic Churches. I can go to Mass in any Catholic Church and know that the scripture is the same one that is being read in my home parish.
The second part is the Liturgy of the Eucharist. This is where the bread & wine become the body & blood, soul & divinity of Jesus Christ.