Sunday Mass is required, and weekday Masses (including Saturdays during the day) are optional.
We are still required to go to Sunday Mass even if we attend Masses during the week, because Sunday is our official day of worship. The Saturday vigil Mass “counts” for Sunday, however, and typically has the same readings and prayers as the Sunday Mass. (Exceptions include Easter Vigil and Christmas Eve, but these Masses still “count” towards their respective obligations.)
Once you develop the habit of attending Mass on Sundays, it will become simply routine to fulfill it weekly.
One way to help yourself with the transition into this good habit is to tell yourself, “I get to go to Mass on Sundays,” instead of “I have to go to Mass on Sundays.” It’s only a way of wording it, but even so, it really does help. After you’ve been going for about a year or so, you will even forget that you ever had anything else to do on Sunday mornings; it will have become an ingrained part of your life.