Explanation
The WORKDAY.INTL can calculate a date in the future or past that respects holidays and weekends. To specify which days are considered weekends, you can use a special code (full list of codes here) or use a "mask" to indicate weekends with ones and zeros. The mask method is more flexible since it allows you to designate any day of the week as a weekend (i.e. non-working day). For example:
=WORKDAY.INTL(A1,3,"0000000") // no weekends
=WORKDAY.INTL(A1,3,"1000000") // weekend = Mon
=WORKDAY.INTL(A1,3,"1100000") // weekend = Mon+Tue
=WORKDAY.INTL(A1,3,"1110000") // weekend = Mon+Tue+Wed
The weekend argument is supplied as 7 characters that represent Monday-Sunday. Use one (1) to indicate a weekend day, and zero (0) to indicate a working day. Since we want all days of the week to be considered working days, we use "0000000".