Today, 9 July, is a feria (weekday with no feast occurring) in the 1962 kalendar. This means that green vestments are worn and the priest repeats the Sunday Mass and readings. However, on a feria the priest may also choose to celebrate a votive Mass, which is a Mass of devotion (of the Holy Trinity, St. Joseph, the Angels, the Holy Eucharist, the Great High Priest, etc.) or for a special need (for the sick, for protection against the heathen, etc.). If he does this, he will generally announce this prior to the start of Mass. You would then turn to the votive Mass section of your missal and find whatever Mass he announced. Vestments would not be green.
On Saturdays that have no special feast, normally a Mass of Our Lady is said. You would go to the common of saints section of your missal and find Masses of the BVM on Saturday, and the correct Mass for what time of year it is. White vestments would be worn.
Another option on a feria is that the priest may celebrate a Mass for the Dead. He would anounce which Requiem he is celebrating (for all the departed, for departed bishops, priests, popes, servicemen, etc.) Black vestments would be worn.
Having said all this, I can tell you that in the old missal, there are more feast days than feria days. For example, tomorrow, 10 July, is the feast of the Seven Holy Brothers, martyrs, with a commeoration of Sts. Rufina and Secunda. You would find these under the proper of the saints. Some of these Masses are proper that that particular feast day, while others are a template form (“common”) of Mass that is used for all the saints of that particular class (all martyrs, all virgins, all abbots, all confesssrs, etc.). In this case, the proper of saints will tell you to turn to page X in the common of saints, which is where these “templates” are.
It is a little confusing at first, but eventually it will be second nature.
