The module called calendar allows you to output calendars and provides additional useful functions related to the calendar. By default, these calendars have Monday as the first day of the week, and Sunday as the last (the European convention).
The 4 parameters are 2018,2,1,6.
2018 is the year , 2 is the width in character of each date and 1 is the number of lines used for a week and 6 is the space between 2 months.
The first day of the week is Monday by default which is given by 0. If you want to change it to Sunday then type the above command. Now the value becomes 6 which stands for Sunday.